Warm Outlets: How Warm is Too Warm?

[uncle_bob]

Hi

Ok, we'll try this one more time:

If the roaring flames are raging through the house and they hit the plastic nut, it melts and shorts. The insulation on the mains wires also melts and shorts. That's all fine and pretty much expected. Through the raging inferno, the copper crimp sheath over the tightly twisted ground leads does not melt. The twisted ground leads can not come apart. The ground circuit out lasts the rest of the system as the fire rages on (as it should).

Bob

No connector in use that I am aware of uses the insulation to maintain contact, including wire nuts. Want to try again?

Read what I said, the plastic melts and the wires short. Using insulation to maintain connection was *not* mentioned above.

[IanB]

If the roaring flames are raging through the house and they hit the plastic nut, it melts and shorts. The insulation on the mains wires also melts and shorts. That's all fine and pretty much expected. Through the raging inferno, the copper crimp sheath over the tightly twisted ground leads does not melt. The twisted ground leads can not come apart. The ground circuit out lasts the rest of the system as the fire rages on (as it should).

Forgive me for being confused, but if the house is a raging inferno the integrity of the electrical ground system is about the last thing I care about...

[Monkeh]

Hi

Ok, we'll try this one more time:

If the roaring flames are raging through the house and they hit the plastic nut, it melts and shorts. The insulation on the mains wires also melts and shorts. That's all fine and pretty much expected. Through the raging inferno, the copper crimp sheath over the tightly twisted ground leads does not melt. The twisted ground leads can not come apart. The ground circuit out lasts the rest of the system as the fire rages on (as it should).

Bob

No connector in use that I am aware of uses the insulation to maintain contact, including wire nuts. Want to try again?

Read what I said, the plastic melts and the wires short. Using insulation to maintain connection was *not* mentioned above.

Through the raging inferno, the copper crimp sheath over the tightly twisted ground leads does not melt. The twisted ground leads can not come apart. The ground circuit out lasts the rest of the system

The steel insert inside the wire nut does not melt, either. In fact, the copper will melt first! The heat will of course affect the properties, but it should not do so particularly quickly.

[forrestc]

I never actually said they're bad, I said if they're considered unsuitable for joining one conductor I cannot see why they're suitable for any other. If they're so bad they cannot be trusted for ground, why can they be trusted where they're actually exposed to current flowing and continual heating and cooling cyles? That's actually arguing in favour of them, or at least trying to be neutral..

Having just recently started using crimps on the ground wires, I can see the benefit of the crimp sleeves.    They connect the (normally bare) copper ground wires much more easily and securely, and more importantly, permanently.   I can't say they're better or worse than wire nuts.

For the record, unless it's a *very* recent change, I don't believe the NEC actually requires crimp for the ground connection in an electrical box.  I searched through my copy of the NEC, and searched through the major changes in 2014, and couldn't find this requirement.

[forrestc]

Crimping is actually considered unsuitable for solid-core wires of any reasonable size by most standards.

Crimping is another area which is asking for problems.  With a correct crimp tool and lug pretty much any wire of any description can have a crimp lug attached.   The problem is that once you get to a reasonable sized solid cable, suitable crimp lugs and crimpers are hard to find and not easily obtainable.

BUT... I will take a properly applied crimp over a soldered and/or screw-terminated (aka clamp) wire any day.   It should be noted that a properly applied crimp is one which has had enough pressure applied consistently around the crimp that the crimp effectively becomes welded to the conductor through pressure.

[djacobow]

I can't say they're better or worse than wire nuts.

This is getting to the point I was trying to make before. Crimps might be better than wire nuts, but how much better _can_ they be? It's not like badly installed wire nuts burning down a houses on every block. We're way down in the noise.

[Xplode]

I guess I'll weigh in again now that we're totally off topic (but the OP seems content).


I've come across wire crimps in residential wiring (here in Canada) but it was all 30+ years old.   We've moved away from crimps and I'm glad.   Wire nuts are the best way to go, period.   I've had to cut off the bonding crimps in boxes before to make changes to the wiring and it leaves me with even less copper to make the re-connect with.    Wire nuts can be backed off, a 1/4 back-turn of the conductors bird-cages them slightly, and you can twist the new conductor into the group.   Minimal fatigue strain on the copper, and a nice solid twisted connection with significantly more copper in contact with copper than a small crimp.  I realize this is because I'm doing the connections properly, creating a "mechanically solid" connection (which is dictated by our NEC) before the wire-nut is applied.    It is absolutely permanent if left untouched for years.   

I don't personally see the connection with the fire concerns of nut vs crimp, but I am curious to see this "welder test" 

Going waaaaaay back in the thread - the 20A 5-20P suggestion is valid.   NEC usually dictates no more than 80% rated load connected to a breaker unless the breaker is explicitly identifies as having 100% rating (which i haven't seen one yet).     so a 15A circuit is max loaded to 12A (way more than this light in question), and a 20A circuit is good to 16A (barely but all good).

Since I don't do residential construction myself, i'm not 100% sure on this, but I believe our local codes have changed in the past few months to start pushing back towards using Armored Cabling or conduit for some of the wiring as we're now required to use Arc-Fault Circuit Interrupting Breakers in sleeping area related circuits.   I was told that we're now required to have mechanically protected wiring up to the ARC fault device (which is usually a receptable - similar to a gfci outlet) and then downstream of that you can use standard non-metallic sheathed wire again.

The devices that scare me are the wire nut replacements that are gaining traction here.  they're a push-in style connector with 3, 4, or 6 wire connections but they're the same idea as the push in connector on a receptacle.   Just a little sprung pin pressed against the wire.     Put that in the welder test and see how it holds up.  Sheesh.   Plus almost every one I come across has bare copper sticking out the back of it, which is extra scary since 90% of my work is done energized. Click for Scary

[Monkeh]

Going waaaaaay back in the thread - the 20A 5-20P suggestion is valid.   NEC usually dictates no more than 80% rated load connected to a breaker unless the breaker is explicitly identifies as having 100% rating (which i haven't seen one yet).     so a 15A circuit is max loaded to 12A (way more than this light in question), and a 20A circuit is good to 16A (barely but all good).

And this is where I think the NEC is utterly stupid. Is it 20A or not? ... apparently not. Insanity.

The devices that scare me are the wire nut replacements that are gaining traction here.  they're a push-in style connector with 3, 4, or 6 wire connections but they're the same idea as the push in connector on a receptacle.   Just a little sprung pin pressed against the wire.     Put that in the welder test and see how it holds up.  Sheesh.   Plus almost every one I come across has bare copper sticking out the back of it, which is extra scary since 90% of my work is done energized. Click for Scary

They actually work very well. No copper is exposed unless people use them wrong (they have strip length markings!).

They will go on the welder as well, I plan to chain assorted connectors and apply as much current as I can sustain (>120A easily), see if any connector becomes loose or heats significantly faster.

[Xplode]

Going waaaaaay back in the thread - the 20A 5-20P suggestion is valid.   NEC usually dictates no more than 80% rated load connected to a breaker unless the breaker is explicitly identifies as having 100% rating (which i haven't seen one yet).     so a 15A circuit is max loaded to 12A (way more than this light in question), and a 20A circuit is good to 16A (barely but all good).

And this is where I think the NEC is utterly stupid. Is it 20A or not? ... apparently not. Insanity.

The devices that scare me are the wire nut replacements that are gaining traction here.  they're a push-in style connector with 3, 4, or 6 wire connections but they're the same idea as the push in connector on a receptacle.   Just a little sprung pin pressed against the wire.     Put that in the welder test and see how it holds up.  Sheesh.   Plus almost every one I come across has bare copper sticking out the back of it, which is extra scary since 90% of my work is done energized. Click for Scary

They actually work very well. No copper is exposed unless people use them wrong (they have strip length markings!).

They will go on the welder as well, I plan to chain assorted connectors and apply as much current as I can sustain (>120A easily), see if any connector becomes loose or heats significantly faster.

The 80% rule doesn't mean the circuit can't handle 20A.  It is fully rated to deliver 20A, but you may experience nuisance tripping, or faster wear due to running at 100% load all the time.   How many people here would buy a power supply rated for 20A and run it at 20A all day and think that was a good idea and that it would be reliable and last forever?   Not many I'd think.   The goal of the breaker ratings is to protect the wire.  Therefor the breaker will trip above 20A to prevent damage and a potential fire, it does not mean you should load the thing up to max capacity, nor does it offer protection for the end device being powered.

The idea of the push-in style nut is ok, but in reality I see lots of problems.   Even with the strip guide markings, the act of pushing the bundled wires back into the box cause the whole bundle to rotate slightly and this action will cause some wires to experience pressure into the device, and others to experience pull outward from the device.   this outward force pulls the wire back out of the nut and exposes copper.   Trust me, Push a bundle in and out of the box a couple times and you'll start to see copper.   Its not a good product in my eyes.   Plus, the tabs in the back of receptacles fail all the time due to heating issues, what makes these any different?  They're produced just as cheaply.

[Monkeh]

The 80% rule doesn't mean the circuit can't handle 20A.  It is fully rated to deliver 20A, but you may experience nuisance tripping, or faster wear due to running at 100% load all the time.

If it's only good for carrying 16A continuous, it's only good for 16A. You can pull a couple hundred amps through it for a short duration, so let's call it a 200A circuit.

We do not have nuisance tripping or 'faster wear' by using a circuit to its nominal capacity.

[Xplode]

The 80% rule doesn't mean the circuit can't handle 20A.  It is fully rated to deliver 20A, but you may experience nuisance tripping, or faster wear due to running at 100% load all the time.

If it's only good for carrying 16A continuous, it's only good for 16A. You can pull a couple hundred amps through it for a short duration, so let's call it a 200A circuit.

We do not have nuisance tripping or 'faster wear' by using a circuit to its nominal capacity.

You can have nuisance tripping.  You've got 18amps plugged in running constantly, and then someone plugs in a 2A load with a bit of inrush, and bam you end up with a tripping breaker.
The breaker does wear itself down when it opens under load.   It draws an arc inside and wears at the contact points.   Its obviously worse under a fault condition, but it still occurs if there's any load at all.   Breakers that have been manually turned on/off lots, or experienced lots of tripping show up on thermal scans ahead of their less abused counterparts.  This is often why.

Circuit breakers are primarily heat based devices.   Controller the thermal loading of a panel in a residential home is pretty difficult.  I have to lower the ratings on every piece of electrical equipment if the temperature is known to be higher than 30C in the area due to this.  Some homes are going to have air conditioning and it helps cool the panels while others are going to have the panel next to the furnace in a mechanical room where the temperature is 30C all day.   

Your option would be to say that this 16A rated circuit but it is ok to overload, sometimes... just be careful you know.   since its really ok to pull 20A through it, but it probably won't trip until you're at least 125% OVERloaded...  this sets a more dangerous precedent than saying "stay under the rating"

There's clearly arguments to both sides of thinking, and i doubt we're going to change your opinion on how the circuit should be labelled, but I think it makes sense, and is safer for the general public, the way it is laid out now.  Besides, that's the electrical code for the installer, not the end user.    The end user can run 20A all day if they want, but they're probably going to experience tripping more often than their neighbor.

If you really want to dig into the electrical codes It gets even more confusing when you start to look at the fact I can put a 50A breaker on a #12awg wire when I'm powering up a 20A motor load.   I certainly wouldn't call it a 50A circuit, since the load is only around 20A once the motor is running, but it needs to survive that inrush current so its got a nice big breaker.   and if the motor can't successfully start on that 50A breaker, I'm allowed to put a 60A on it.   Still not going to call it a 60A circuit though.   That's insanity.

[Monkeh]

You can have nuisance tripping.  You've got 18amps plugged in running constantly, and then someone plugs in a 2A load with a bit of inrush, and bam you end up with a tripping breaker.

Not a problem we regularly face, oddly..

The breaker does wear itself down when it opens under load.   It draws an arc inside and wears at the contact points.   Its obviously worse under a fault condition, but it still occurs if there's any load at all.   Breakers that have been manually turned on/off lots, or experienced lots of tripping show up on thermal scans ahead of their less abused counterparts.  This is often why.

And that has nothing to do with loading to nominal rating. Either it's capable of handling it or it's not. Your breakers may suffer from being loaded to nominal and tripped; that's because they're only actually designed for 80%, and the label is, uh, optimistic. It's marketing bullshit, just like '20V' batteries for tools.

Your option would be to say that this 16A rated circuit but it is ok to overload, sometimes... just be careful you know.   since its really ok to pull 20A through it, but it probably won't trip until you're at least 125% OVERloaded...  this sets a more dangerous precedent than saying "stay under the rating"

.. no, my option is to have a 16A circuit which can handle 16A continuous. No breaker trips magically exactly 0.1A above its rating. They have thermal and magnetic trip profiles, and all breakers in ROW are set to allow operation at nominal current. And cable is appropriately sized.

If you really want to dig into the electrical codes It gets even more confusing when you start to look at the fact I can put a 50A breaker on a #12awg wire when I'm powering up a 20A motor load.   I certainly wouldn't call it a 50A circuit, since the load is only around 20A once the motor is running, but it needs to survive that inrush current so its got a nice big breaker.   and if the motor can't successfully start on that 50A breaker, I'm allowed to put a 60A on it.   Still not going to call it a 60A circuit though.   That's insanity.

But it is a 60A circuit. Or at least 80% of one.

Again, in ROW, we have breakers with trip profiles. They are selected according to the type of load, and the cabling used is calculated and tested to ensure safe operation of the breaker over fault conditions.

[Xplode]

You keep implying that our breakers don't have trip profiles, but they obviously do.   And they have Interrupt ratings in the 10kA to 100kA+ ranges so that they can operate safely in a fault situation (so long as available fault current was considered during product selection).   None of this is really the question at hand.   

The trip profiles dictate that the breakers will trip once you go over the marked rating, same as I suspect yours do.    if you're .1A over the rating its probably not going to trip since that's such a tiny amount over it could easily be lost in the manufacturing tolerances.    However, it may after a while.    It'll probably take a while, but it might.   I'd call this nuisance tripping, since while it is technically overloaded, it isn't anywhere near dangerous and it certainly isn't a fault condition.    However, this would all be avoided if you simply stayed under the breaker rating.   Doesn't matter where you are in the world, if you stay under the rating it should never trip.   Plus it gives you some wiggle room for loads that might fluctuate.   Since breakers are thermal devices, having a row of breakers in a panel that are all operating at their max rated load increases the odds of a trip as well, altering that trip curve you keep talking about.    If its the only breaker with a load on it, then it will be less likely to trip since the heat can dissipate through the electrical panel, bus bars, wiring and other breakers.  Hence the ambient temperature rules I need to consider in warmer environments.

We also have different types of breakers and fuses, each with their own operating characteristics and ideal use situations.  My comments have been based on the generally used residential style thermal type breaker since that's what the original post was about (residential installation).   In an industrial location I probably wouldn't be feeding a motor with a residential style breaker as usually they aren't HRC rated and the services are much larger.   If I had to use a breaker with a big industrial load, I'd likely use a breaker with the ability to adjust the magnetic trip profile to prevent tripping on inrush.   I was simply highlighting that there is lots of variations in the code rules, developed to allow an educated (hopefully ) and trained person to maximize the installation and keep the costs reasonable without compromising safety.  The 60A breaker mentioned does not make the circuit 60A capable in the eyes of the code (or any of the installers on this side of the pond).  It would still be based off the calculated values of the wiring, minus any derating factors such as high ambient temperatures, conduit fill, and distance.   


It is interesting what you are saying about your 16A circuits delivering that all day without trouble.   At what point do they start to trip when overloaded?   I'm actually kind of curious to compare the trip curve graphs of the two now.

[Monkeh]

The 60A breaker mentioned does not make the circuit 60A capable in the eyes of the code (or any of the installers on this side of the pond).  It would still be based off the calculated values of the wiring, minus any derating factors such as high ambient temperatures, conduit fill, and distance.

So then how do you identify the actual current carrying capability of the circuit after the fact? Measure the conductors, inspect every inch of the installation? ... or just use a breaker with a nominal rating to match the circuit capability.



Pretty much infinite.. and yes, a B16 can take 20A continuously. So can the wiring it's used with. Wiggle room: We build it in and get circuits which do what they say on the tin.

E: For reference, 2.5mm² hardly even gets warm in open air at 60A for 40 seconds.

[IanB]

What is also not being mentioned is that circuits are often wired differently in the UK. For instance a standard UK socket is rated for 13 A at 240 V and thus can supply 13 x 240 = 3000 W continuously. Plenty of devices like electric kettles or space heaters are manufactured that consume exactly 3000 W, are fitted with a plug containing a 13 A fuse, and are expected run as long as you like without anything tripping. This works because the wiring behind the wall socket and the breaker in the panel are both rated for substantially more than 13 A. The fuse in the plug protects the appliance flex and the circuit is not close to its limit.

Of course if you plug several 3000 W devices into the same circuit all at once then you may trip the breaker, but with a typical distribution of loads this doesn't happen (unless the WI is holding a social event and wants to brew cups of tea for 30 people all at once...)

[Xplode]

So then how do you identify the actual current carrying capability of the circuit after the fact? Measure the conductors, inspect every inch of the installation? ... or just use a breaker with a nominal rating to match the circuit capability.

Any electrician worth his salt is going to inspect the circuit installation if he intends to do any alterations to the breaker sizing anyway.  So yes to the first part.    It also means I don't need to run a large wire to the load just to get it through its startup.    Since we're on opposite sides of that big ol ocean, I have to admit i'm not well versed in the mm² equivalents of our AWG sizing, but to run a 60A wire to my hypothetical motor load, versus a 20A wire (which actually carries a 30A rating for motor loading) there is a significant cost difference, not just in the actual copper wiring, but also in connectors, straps, etc.  It all goes up.   Its just not efficient use of resources to do that.    So we are allowed by code to use a breaker of up to 250% the FLA rating on the circuit, regardless of the wire sizing.   The wire sizing is a separate calculation (has to be >125% of the FLA to help accommodate the expected inrush).  If that breaker can't support the motor getting through its startup, then I can go go up a size.    This is simply to allow the trip curve to support the startup of the motor, but then still cover the wire in a fault situation (at which point the trip curve is near instant anyway, even without a magnetic element).   So at the end of all that, there is no one here that would consider that circuit as rated at 50A or 60A, even though the breaker would technically allow it if you tried.   On bigger motors in industrial locations, they're usually fed via a Dual-Element/Time Delay style fuse anyway.    Then the sizing is lowered to 175% of the FLA rating.

As for the trip curve graph you posted, I will have to try and dig up something from a local vendor this evening and post it up for comparison.   It's dinner time here and I'm starving

[IanB]

Since we're on opposite sides of that big ol ocean, I have to admit i'm not well versed in the mm² equivalents of our AWG sizing

2.5 mm² is about 13 AWG

[Monkeh]

So then how do you identify the actual current carrying capability of the circuit after the fact? Measure the conductors, inspect every inch of the installation? ... or just use a breaker with a nominal rating to match the circuit capability.

Any electrician worth his salt is going to inspect the circuit installation if he intends to do any alterations to the breaker sizing anyway.

Who said anything about altering the breaker? If it's got a 60A breaker, why should it not be able to have a 60A load? Why should it be allowed to have a cable so small a continuous 60A load from a fault could be a hazard?

to run a 60A wire to my hypothetical motor load, versus a 20A wire (which actually carries a 30A rating for motor loading)

You don't need to run a 60A wire. You need to run a wire capable of handling the prospective fault current until the chosen breaker is ensured to trip, without becoming hazardous.

[Towger]

So in the states you don't have different mcb/breaker types to handle higher inrush currents, you just use a much higher rated breaker?

[Xplode]

If you're not altering the circuit, why would you even ask about inspecting it?   The motor loads are monitored at the motor starter for excessive loading that is specific to that motor's FLA (usually adjustable via interchangeable heating elements, or trim pot on electronic units).    The only situation that should cause that breaker to trip is a fault, which it will have no problem handling since the current will jump drastically above the ratings and trip out the magnetic elements (assuming proper grounding, if the fault is ground related).    The breakers are going to clear a fault before the wire can heat up to any dangerous level anyway, even with the increased time curve of the over sized breaker.    So I think despite the circle we've gone in, we both are agreeing on the same underlying foundations for the safety of the installation design anyway. 

I dug up a manufacturers Time Current Curve graph (Siemans Residential Breakers) but its pdf, sorry couldn't find a jpg.    This is a common breaker used currently in residential and commercial installations for general purpose circuits. 

It looks like your breakers don't trip when they're supposed to, which seems odd to me.   If I'm reading that chart right, it looks like at 23A the B16 would take around an hour to trip out.   That seems more dangerous to me than a breaker marked 20 that will trip out after 5-10 minutes.  Why does it make sense to have a 16A breaker that doesn't actually function reasonably quickly once you're over that rating? Our wiring is apparently larger than yours from the sounds of it too (#12 is about 3.3mm²).    So the North American 20A breaker can deliver the rated power, and is backed up by larger wiring for the fault currents that you mentioned, plus won't get as warm at the 23A in this example.    (which is technically overcurrent in both setups).  I will agree that to a homeowner, the faster tripping is far more inconvenient, but its not safer to let it run longer.

There's too many differences in the way the power is distributed to probably say one is truly better than the other anyway. Especially since it sounds like you guys have different physical sized wiring available to you.  I actually like the fact that you guys get higher voltages - lowers the line loss after all!  But ours does hurt a little less when you do something stupid .   But you guys get more horsepower per circuit... I've been curious about European power systems  for a while, just never had the chance to really educate myself on it.    One post a few back leads me to believe you guys have fuses right at the receptacles???   Also, since you guys use a grounded earth system (that right?), is it a 230V to earth setup with a Hot Line/Neutral/Ground configuration or a Line-to-Line with earth?  And if its the first, do you have two Lines coming in for your services or just one? (ie 460v Line to Line?)

[Xplode]

So in the states you don't have different mcb/breaker types to handle higher inrush currents, you just use a much higher rated breaker?

I'm in Canada, so I can't say for certainly how the US Electrical Code says it is to be done.   But that's a complicated question.
It depends entirely on the installation and surrounding factors like voltage available, horsepower requirements, etc.

In a small operation, they may only have single phase power so its probably going to be a standard residential style breaker.   So there aren't really multiple types to pick from, you just use what is certified for use the panel and the code allows us to go larger.   The current draw is marked on the load, and since its not possible to just plug something extra in to the circuit, it is considered a calculated load and so a larger breaker isn't really a risk since the wire will never continually supply more than its rating.  Fault currents are massively larger than the rating, so easily cause the trip elements to function quickly before the wires become dangerous.

   In a situation where three phase power is available, you may have choices on the types of breakers.   When working in larger installations, we often have Motor Control Centers (MCCs) that allow us to rack in whatever type of circuit protection we need.  This is usually only available at higher voltages like 460V or 600V (or higher) though, but in those cases, we can use motor rated CBs or Time-Delay Fuses.     

It really does come down to fault currents.   In smaller voltages and currents the power required to be dissipated is significantly lower than at higher voltages and currents.

[IanB]

I've been curious about European power systems  for a while, just never had the chance to really educate myself on it.

Europe varies widely in electrical systems. You have to look at each country separately.

One post a few back leads me to believe you guys have fuses right at the receptacles???

In the UK appliance plugs have a replaceable fuse (the plug, not the socket). Most of the time it is a 13 A fuse, but some appliances like lamps will be fitted with a 3 A fuse.

Also, since you guys use a grounded earth system (that right?), is it a 230V to earth setup with a Hot Line/Neutral/Ground configuration or a Line-to-Line with earth?  And if its the first, do you have two Lines coming in for your services or just one? (ie 460v Line to Line?)

In the UK the 240 V supply is Live/Neutral/Earth with 240 V on the Live relative to Neutral/Earth.

The 240 V supply is almost invariably derived from a 415 V three phase transformer with each 240 V circuit made from one of the phases and the neutral. Most homes only receive one of the phases, but larger premises and commercial properties might get all three phases especially if they have large loads.

The split phase arrangement found in North America is not found in the UK except on construction sites where electric tools are supplied by a 55-0-55 center ground supply.

[Xplode]

Interesting!   Thanks for the details.

So the tools are actually 110V tools, same as here?  That's interesting.    Any reason they aren't made to match the local standards?   Seems like an inconvenience to have to wire up transformers for temporary power on construction sites.   

[IanB]

So the tools are actually 110V tools, same as here?  That's interesting.    Any reason they aren't made to match the local standards?   Seems like an inconvenience to have to wire up transformers for temporary power on construction sites.   

The tools thing is for safety since the maximum voltage to ground is 55 V, but this is only for commercial tools on construction sites. It's no inconvenience since such tools do match the local standards for that environment. The tools and transformers do not have to be specially made, they are standard items.

Home use tools run off 240 V just like anything else though.

[Xplode]

So the tools are actually 110V tools, same as here?  That's interesting.    Any reason they aren't made to match the local standards?   Seems like an inconvenience to have to wire up transformers for temporary power on construction sites.   

The tools thing is for safety since the maximum voltage to ground is 55 V, but this is only for commercial tools on construction sites. It's no inconvenience since such tools do match the local standards for that environment. The tools and transformers do not have to be specially made, they are standard items.

Home use tools run off 240 V just like anything else though.

I guess I meant the local standards used everywhere other than the job site.
Guess  you can't take the tools home and use them then huh.   That seems kind of annoying having to own multiple versions of the power tools, but I suppose that means you aren't required to use Ground Fault Detection circuits on the job site?