Electronics > Power & Renewable Energy

How to get more than rated current from 240v home GPO sockets?

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ZeroCubic:
Hi guys, first time posting so apologies if this has been discussed elsewhere or if I should be posting in a different topic area.

About me: I live in Australia. I work in robotics as a contractor design engineer.

The Brief: I am working on a project which requires casting metal parts from 3D printed molds, and sintering 3D printed metal powder objects. For this I need an electric muffle furnace which goes to 1700c and can hold a hydrogen atmosphere (luckily alibaba has them at a good price). This will be installed at an office which has only 240v 10A sockets.

A furnace with the specs I need requires 4kW of power continuously.  Clearly a 10A socket at 240v can't do this. and even a 15A socket (which I dont have anyway) can't either (3600W).

So is there any practical way of getting 4kW of power (for up to 48hours, for some refractory metals, so generator is out) without having 3 phase installed?

My ideas so far are:

Idea 1: Couple 2 or 3 powerpoints together (each on separate circuits) into a single 20A single phase? I don't have much experience with AC power circuits but my intuition is telling me if I simply wire them together directly they would get out of phase and do something unpleasant and not work. Is there a specialised circuit I don't know about which is designed for this sort of thing?

Idea 2: take a feed directly from the distribution box, use high amperage cable, and install a 20A fuse. I imagine as long as the distribution box can handle 30A total (the furnace + other devices running concurrently) I dont see why this wont work. Also I dont know how to tell what the maximum current my distribution frame can handle; it isn't written anywhere obvious.

If anyone familiar can tell me why this wont work and if there is another way that will work, I would be very grateful

for the curious, this is the kind of furnace I'm talking about: https://www.alibaba.com/product-detail/1700C-laboratory-chamber-H2-hydrogen-CH4_62361982245.html?

james_s:
What is the capacity of the circuits you have available? I have only very limited knowledge of Australian electrical codes but electrons behave the same anywhere. Forget about the sockets you have, none of those are adequate for such a large load. If the circuit is wired with sufficiently heavy cable then you can either install a socket of sufficiently high amperage rating or you can hardwire the furnace. A better option if you are able to do so is install a dedicated circuit with the breaker and wire sized to handle the load and run it directly to the location where the furnace is. Here code would require a dedicated circuit for a large appliance like that, I don't know what your local codes say but one of our Australian members can probably provide more info.

NiHaoMike:
You could use a transformer on each circuit to turn the 240V into 120V at double the current, then connect the two in series. Transformers that big are going to be heavy and expensive.

--- Quote from: ZeroCubic on September 08, 2021, 01:55:47 am ---Idea 2: take a feed directly from the distribution box, use high amperage cable, and install a 20A fuse. I imagine as long as the distribution box can handle 30A total (the furnace + other devices running concurrently) I dont see why this wont work. Also I dont know how to tell what the maximum current my distribution frame can handle; it isn't written anywhere obvious.

--- End quote ---
That's the right way to do it, read the label inside the access door to find out the rating, then check the size of the main breaker. In addition to the new breaker and wiring, you'll also need a disconnect for servicing the equipment, that can be a properly rated plug and socket or a disconnect box.

james_s:
Using transformers is a kluge at best and probably not legal, even if you connect lower voltage secondaries in series there is the possibility of backfeeding a circuit that has been shut off at the breaker/fuse, this is not going to be safe and probably is not legal.

No matter what you do you are going to be limited by the maximum capacity of the panel since all of the circuits are in there. I would be very surprised if the capacity is not well over 30A. What is it fed from? Surely there must be a main breaker somewhere, if not in the panel itself then upstream. What size wire is feeding it?

Check the local codes in regards to the need for a disconnect at the equipment, I'm fairly confident it will be permitted and it is probably a good idea, but it may or may not be required.

David_AVD:
A typical power circuit in a vaguely modern office should be rated at 20A. That's 4800W @ 240V.

Depending on what else is on that circuit, you may be able to have a 20A outlet fitted.

The better solution is to run a new dedicated 20A circuit just for the purpose.

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