30A wiring advice

Don't even thing about it.

If your #10 gets disconnected, the circuit opens. No problem. If one strand of your double #12 gets disconnected, your house burns down. Problem.

Actually, it is okay to thing about it; just don't think about it. (fingers faster than brain, sorry.)

UK regs allow it providing each conductor has its own current protection. In the case of more than 2 in parallel, protection is required at both ends of the parallel run, as fault current can be back-fed too, via the other parallel conductors. Having said that, you'd have to be nuts to do all that just to save using the right sized conductor in the first place.

The NEC is pretty clear about parallel wiring in section 310-4. 1/0 (that is one/zero) and larger are allowed to be paralleled. Smaller is not allowed unless it is for instrumentation.

I can't think of any place in the world (except maybe the African jungle) where you can't find #10 wire or something equivalent.

In any case, this reminds me of some 'African engineering' I did to my electric oven one time. One evening, my oven suddenly stopped working. After looking in the back to see what might be wrong, I found that one of the wires somehow burned in two. Instead of going to an appliance parts store and buying the proper part, I just took a cord from an old lamp, cut it into five short pieces, bundled the pieces together and used them to replace the wire that was there. I don't know how safe it was, but it worked. :-)

Robert

My guess is it is the same place where there are not too many noisy inspectors telling you how to build your house.

Sincerely,

Donald L. Phillips, Jr., P.E. Worthington Engineering, Inc.

145 Greenglade Avenue Worthington, OH 43085-2264

snipped-for-privacy@worthingtonNSengineering.com (remove NS to use the address)

614.937.0463 voice 208.975.1011 fax

Sorry, can't help it: Why can't you get #10, when you can get #12?

Do you have a death wish?!? Let me guess you live at the South Pole and supplies are limited. Dude, give me your mailing address and the length of wire and I will frigging send it to you. You can buy online form several suppliers. Or better yet call a qualified electrician!!!

I just knew I would get asked about the supply problem!!! I live in Switzerland now. The heavier wiring is simply not available in the DIY shops here - its probably a safety precaution by the authorities, also Switzerland supplies approx. 380V/220V to each dwelling so large gauge wires are not really essential.

The dryer works fine following some modifications I made - basically disconnecting internal 120V circuits that only served to provide some advanced functions which we don't miss like moisture sensor based automatic drying. I connected the heating element across a 240V supply and the motor (5.2A, 1/2hp) and timer across a stepped down 120V. But whilst running, the wires do feel a litle warm (note the unit has been running fine for the last

2 years in Switzerland and continues to do so) and this bothers me.

Wade thanks for your feedback, I feel really stupid not having realized that in the first place. I think the best solution will be to get some #8 wire from a friend in the USA.

Thanks everyone. More feedback is of course welcome.

supplies are limited.

frigging send it to you. You

Damned difficult to believe that 10-gauge wire is unavailable in Switzerland. One might simply drive to a neighboring coutry and buy it if it is. Or is CH simply a convenient posting location? In any case, I surely wouldn't mess around with using multiple conductors to overcome the problem -- for all the reasons that others have cited.

How do they supply 380v/220v? Presumably the 220v is single pole. Where does the additional 160v come from?

I guess I should have known that bureaucracy had something to do with this. It seems to me that a law like this would actually increase the danger since it would create the temptation for the do-it-yourselfer to use smaller wire than he should be using.

Robert

How much #10 do you need? I can just mail you some.

OK lets all hold our noses, remember this is not an NEC country and answer the question. If this were a larger size wire you can do this so lets make an HO guage parallel 1/0 connection. To do that you need devices that have terminations rated for 2 conductors. What do the breakers look like? If they are Square D style (floating plate with a wire slot on each side) you will have what you need on that end. What does the dryer have? Can you put lugs on a terminal block for 2 conductors a phase? Logic says you can just twist them together real tight and put them in a single lug (hole with a set screw not under a screw head) but that will not meet the US code. For the life of me I can't see how any logical person could say this was dangerous if the wires were twisted and soldered and that is a pants with suspenders answer. Just be sure any paralleled conductors are the same length, size and composition.

I read in sci.engr.electrical.compliance that Joe 90 wrote (in ) about '30A wiring advice', on Wed, 1 Oct 2003:

All the advice you were given applies, AIUI, to installations in US. In Switzerland, the rules are quite different. What you are doing may even be illegal there. Switzerland controls what is connected to the electricity supply VERY tightly.

You won't get #10 wire in Europe because European cables are described by the conductor area in square millimetres. I don't have a conversion chart from AWG to square mm; for 30 A you probably need 6 mm^2 cable, but it depends on exactly what sort of cable and how it is installed.

After making the original changes 2 years ago, I had the results verified by a local electrician and he was satisfied that there were no potential problems.

However I just recently looked at the wirirng diagrams again and there are two points that I don't understand. I have always understood voltage as being a potential difference. Current flows from a high potential to a low potential. This means that the input to a device has to be at a higher potential relative to the output, typically connected to Neutral or Ground. This would be the case even when using ac current.

Yet when one looks at the power supply in the USA you have a common Neutral and two 120V single phase hot lines. The typical heating element in a dryer in the USA is connected across the two 120V lines (making a 240V supply).

Now my first point is surely if both lines are in phase at 120V then there is no potential difference and so how can the current flow? Or is the current only really oscillating left and right along the wires in sync. with the phase variance, in which case why bother with the neutral (except as a safety ground) in many ac appliances.

120V ------------------------------------- a Neutral ----------------------------------- b 120V ------------------------------------- c

Vab =Vbc = 120V, Vac = 240V - dryer heating element is across Vac.

My second point concerns the wiring ampacity. The dryer is rated at max

30A, so one would expect the heater wires to be AWG 10 (NEC guidelines), but in fact they are AWG 12 (max 20A). Is this because in fact the heater is being fed by two 120V circuits? And does this mean that if I connect a European 240V setup as follows:

N --------------------------------------- d 240V ----------------------------------- e Dryer heater element is across Vde

that these AWG 12 wires are being stressed beyond NEC recommendations?

Thanks in advance for any responses.

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You should not be connecting to ground as a means of providing power flow to anything. Don't confuse neutral (the grounded supply conductor) with Ground (the groundING conductor).

The current in one 120 phase is at opposite polarity (with respect to the neutral) as the other 120v phase. The neutral is there so you can get 120 volts too. You don't want to dry clothes in the dark do you?

Isaac

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First of all, it is most likely not up to code where you might be. With that said, #12 is actually rated for 25 amps under certain conditions. NEC (USA) just requires a 20 circuit protection on it in construction. In panels, we can use the full rating of the wire but must allow for #10 field wiring if between 20 and 30 amps..

Second of all, most likely your load my not be a full 30 amps. If you have a way to do it, test it.

Next, the wires in parallel will have no problem with 30 amps from a technical stand point. Yours is a code issue, which may be a safety issue.

I don't recommend you do it, but there is an answer.