30A wiring advice

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I am making some changes to an electrical dryer. Where I live, I cannot get hold of 10 gauge wire for the 30A circuit - I know, don't ask why, pls. Can I use two 12 gauge wires connected in parallel? Based on my electrical knowledge, this would split the max current between the two wires allowing the wires to run cooler and well below max capacity.
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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.
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faster than brain, sorry.)
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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.
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Andrew Gabriel
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"Andrew Gabriel" wrote in message

Hmm, BS 7671 allows a single overcurrent protective device to be used with parallel conductors provided that:
- the sizing and layout is such as to ensure equal current sharing, and
- there are no branches taken off one of the cables (ring final circuits are exempted from this), and
- a fault anywhere on one of the circuit cables will operate the device without exceeding the relevant conductor temperature limit (adiabatic compliance).
Multiple devices are only required if the above can't be complied with. See regulations 473-01-06 thro' 473-01-08, 473-02-05 and 523-02-01.
But as you say, the design calculations required are well beyond the capability of the average electrician, so it doesn't happen very often.
--
Andy



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Wade Lippman wrote:

didn't notice his house had burnt down. Poor guy.
--
jim

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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.
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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

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(remove NS to use the address) 614.937.0463 voice 208.975.1011 fax
http://worthingtonengineering.com
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Joe 90 wrote:

Sorry, can't help it: Why can't you get #10, when you can get #12?
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Hi, No #8 either? Tony
Robert A. Barr wrote:

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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 am making some changes to an electrical dryer. Where I live, I cannot get hold of 10 gauge wire for the 30A circuit - I know, don't ask why, pls. Can I use two 12 gauge wires connected in parallel? Based on my electrical knowledge, this would split the max current between the two wires allowing the wires to run cooler and well below max capacity.
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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.

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does the additional 160v come from?
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3 phase.... 380 phase to phase gives you more or less 220 phase to neutral
--
obsidian


"Wade Lippman" < snipped-for-privacy@frontiernetnospam.net>
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<snip>
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
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I read in sci.engr.electrical.compliance that Joe 90

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.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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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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I read in sci.engr.electrical.compliance that Joe 90

NOT TO GROUND! That would be deadly dangerous!

They ARE NOT in phase. The fat that you have to ask this question indicates that you are in out of your depth. There is no blame for not knowing, but there IS for dealing with things that you don't know about.
Simple logic would tell you that your assumptions are wrong, because the US system works, whereas you 'proved' it couldn't.

The neutral is very definitely not a safety ground and must not ever be used as one.

Are these wires internal to the dryer? If so, the NEC ampacity tables don't apply, because the installation conditions are different.

No.
No, not if the dryer was designed correctly in the first place. Does it have a UL sticker?

0.005129 sq. in., which is 3.3 sq. mm. As multicore building installation cables, these would, if they were standard sizes, be rated at roughly 30A and 20 A respectively in Europe. But as single-conductor cables, inside an appliance, the current ratings might be MUCH higher (around 43 A and 35 A), depending on the insulating material and the local ambient temperature.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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