Setting up A Workstation in An Old House with Two Prong 120V60AC Outlets

[SiGuy]

Hi!

I am ready to have fun in the electronics world and get away from my real job in signal integrity & pcb design.

I just bought a copy of Learning the Art of Electronics, ordered all the parts thanks to the BOM post on eevblog, bought a Siglent SDS1052DL, a Global Specialties PB-505, and tons of clips and some extra o-scope probes. And am ready to go! Just one potential problem...

I just moved into a rent house and most of the outlets are two-prong... It's an old house built back in the 1940s. Do you guys see any potential problem with this and my setup?

[SiGuy]

I'm thinking I have three "options"

1) Using what I believe are the legitimate three prong outlets after I test to make sure they are actually connected to earth.

2) Use a ground lift adapter on the two prong outlets. I don't think this would do quite so well on the o-scope. I did a lot of reading seeing that they are (or at least components) are connected to earth. Just a WAG right here.

3) Replace the two prong outlets with three prong and have a wire going from the earth GND port and stick in in the ground.

or 4) call an electrician

[gardner]

I would have a look inside the electrical box on some of the outlets to see if if there is a ground in the box.  If the box is grounded you could feasibly upgrade the plug itself to a grounded one and ground it to the box via a pigtail.  If there's no ground in there then your only option is a GFCI/RCD outlet.  If you have a knob-and-tube electrical system, you're hosed for a ground.  You won't even know which lead is hot.

Where I live, a place with that old an electrical system would not meet basic building safety requirements to be rented out as a residence.

[SiGuy]

Thanks for tip^^^ and...

Damn. Damn. Damn. 

Popped open the fuse box... tubes... I'll have a talk with the landlord. Kind of unreal that it's still this old. Nice lady but really? I wonder if this means a whole rewire? My first thoughts is a lot of cash and a certified electrician.

Worst case I can setup at the lab that I work at. They won't mind.

Besides this, is there real issues here with this setup that I am trying to do with my old home circuitry?

[gardner]

Read up on "gfci without ground wire" in google.  I think you could install your own GFCI outlets alright, as long as you can disconnect the supply somehow via a breaker or fuse.  You'll need a non-contact voltage detector, most likely, to identify the hot vs neutral.  With K&T, I don't think you can trust the colour of the pigtails.

[SiGuy]

Thanks guys,

I did some digging.

I found the house had a few gfci outlets, a lot of two prong outlets, and some three prong outlets (at least one in each room). I busted one of each open. Three prong outlet did have a bare copper wire attached to it. This has to be earth ground. The gfci had some sort of a bare copper pigtail but I couldn't tell what it was attached to (maybe the neutral?). And the two prong just had two wires going to it.

In the kitchen there is a fuse box with actual tubes in them. I thought this was what I was going damn damn damn about above ^^^. But then I went outside and saw a general electric box. Opened it up and there was the circuit breaker switches with all the rooms and high power devices on them.

I'm not good with houses yet so here goes a stupid assumption. It seems probable that the old fuse box is just sitting there not in use. I'm also assuming that the reason for the two prong outlets being the majority of outlets all boils down to one thing. Money. $$$.

There's at least one three prong in each room. I'm going to assume that the home owner wanted to cut corners and save some money on here electrician bill when the house was updated. What do you guys think?

From all this, I would think that I'm good as gravy! 

[Tom45]

Just to clarify, the "tubes" in the fuse box are glass screw in fuses? Or do you see porcelain tubes with wire running through the hollow center?

I'm guessing you mean glass fuses in the fuse box. A house built in the 40's is too new for knob and tube wiring.

To see if the kitchen fuse box actually is functional, unscrew the glass fuses and see if anything stops working.

[SiGuy]

http://i.ebayimg.com/images/a/T2eC16F,!)EE9s2ufE9RBR(JOYP-y!~~/s-l300.jpg

This is one of the screw ons in the kitchen box

[Tom45]

http://i.ebayimg.com/images/a/T2eC16F,!)EE9s2ufE9RBR(JOYP-y!~~/s-l300.jpg

This is one of the screw ons in the kitchen box

That link isn't correct.

Is this what you have? http://homerepair.about.com/od/electricalrepair/ss/fuse_types.htm

[SiGuy]

Yup. Thats the one.

[helius]

Open the outlets to see whether they are grounded. If armored BX cables were used, they are grounded inside even if only 2 prong sockets are used. This is what the "green wire" adapters are intended for (you screw the green wire into the faceplate, and it makes a ground connection through the cable shield). If unshielded wire with porcelain insulators was used ("cap and tube"), there is no ground connection and using adapters is not safe.

[Sceptre]

1.  The knobs and tubes in knob-and-tube wiring would be in the walls or attic.  See http://knobandtubewiring.com/ for examples.  This is separate from the glass/ceramic fuses that you found in the kitchen panel.
2.  My guess is that the kitchen fuse box is a subpanel to the outside breaker panel.  The fuse box supplies the two-prong outlets while the breaker panel supplies the three-prong outlets (they saved money by not rewiring everything).  You can readily test that by pulling fuses or turning off breakers and checking which outlets go dead.
3.  Per thread at http://www.electriciantalk.com/f5/ac-bx-cable-ground-65084/index2/:  "BX with the thin metal strip in it can be used as an equipment grounding conductor but the older BX without that metal strip cannot be used as an equipment grounding conductor."  Electricians tend to distrust older BX as corrosion and age compromise the ground connections.
4.  To give you a basic idea of the correctness of the wiring, you can buy a three-prong outlet tester (e.g. https://www.amazon.com/ELECTRICAL-RECEPTACLE-TESTER-OUTLET-PRONG/dp/B002Q3R7HI) and check the various outlets for proper hot/neutral/ground configuration (use a ground lift adapter, with the ground lug screwed tight to the outlet plate, for the two-prong plugs).  This wouldn't prove that the BX on the older outlets could handle a fault, but hopefully the three-prong outlets are correct and will suffice for your workstation.

[steverino]

I've done quite a bit of rewiring of older houses.  1940's wiring is unlikely to have any ground wire.  Occasionally, I've run across a non-integral ground wire that is haphazardly strung from outlet to outlet.  Every time I've seen this, the ground wire, being bare and unprotected, is usually compromised and not continuous.  The wire is typically bonded to a metal pipe and does not terminate at the panel.   You can replace a 2 prong outlet with a GFCI outlet to obtain a safety ground (shock hazard).  Beware that 1940s era wiring used rather small metallic outlet boxes.  If you update to GFCI, use electrical tape around the screw terminals to prevent shorting to the enclosure.  For a stud mounted outlet box, you can replace the box with a SmartBox (trade name of outlet box) if it's too small.

[ez24]

I'm thinking I have three "options"

1) Using what I believe are the legitimate three prong outlets after I test to make sure they are actually connected to earth.

2) Use a ground lift adapter on the two prong outlets. I don't think this would do quite so well on the o-scope. I did a lot of reading seeing that they are (or at least components) are connected to earth. Just a WAG right here.

3) Replace the two prong outlets with three prong and have a wire going from the earth GND port and stick in in the ground.

or 4) call an electrician

You forgot #5  - Do nothing - that is what I did and it has worked for the last 25 years. You may need an 2 prong to 3 prong adapter or a pair of pliers.  You will not die unlike what a lot of people will think.