30A wiring advice

Same thing that would happen in all the other cases where the NEC allows parallel runs and similar to what would happen if the conductor got nicked or partially broken.

Sa

I thought he said he had been running it on #12 for years. I guess he didn't notice his house had burnt down. Poor guy.

Wire insulation. Although it is "self extinguishing", it will contribute fuel if there is an external energy source such as an arc.

Ben Miller

I suppose you might have some burning of some types of insulation but I have to assume that is accounted for in the listing. The fact still remains "electrical" fires are usually started on the customer side of the receptacle, not in the wall.

..or started by debris within the wall cavity contacting bare wires at the rear of the receptacle which were not fully inserted into the receptacle terminals and/or taped off by the installing electrician.

IIRC, rat poo is particularly conductive.. and has started house fires.. but I've never tried it myself.

Cameron:-)

That's why we have a box around that device. There is also a rule against "debris" in the box, flammable wall coverings exposed at the edge of the box, unsealed holes in the box and the composition of the cover. If you had an insulation fire at a termination it should be contained in the device box.

What rules are there on box covers as for wall switches? I see all kinds of craft switch-plates and most of them don't have any UL or CSA markings.

Best regards, Spehro Pefhany

110.3 ... They must be "approved" and that usually means the AHJ sees the listing mark. After something is installed and inspected god only knows what the customer might do but in this "sue happy" society I can't imagine Home Depot selling anything that is not listed. YMMV if you buy something on Ebay.

I will have to look at some of those designer covers the next time I am at the Borg.

I read the replies to your post. I don't get the objections - they seem thin, unrealistic and unsupported to me.

I'd really like to see some support for the concept that putting soldered wire under a screw causes creep. I've never encountered a problem with soldered wire under a screw terminal, and I've seen the dimmers with soldered ends that you describe. On the face of it, it seems the basis for the objection is wrong. But if there is a problem with it, I'd sure like a pointer to that information.

Can't quote any reference as I cannot yet connect brain to internet but long experience has shown it to be true and others in this thread have attested to it as well. Please believe us , it is true.

I read in sci.engr.electrical.compliance that s wrote (in ) about '30A wiring advice - a complication?', on Wed, 1 Oct 2003:

Well, I'm a Chartered Electrical Engineer, living and working in UK, and although your detailed explanation is correct, that IS the description of a two-phase system.

Just as the phase angles between the conductors of a 3-phase system are

120 degrees, so that the three angles add to 360 degrees, the angles between the phases of a 2-phase system are 180 degrees, adding up to 360 degrees.

I agree that solder is softer than the copper and it will be extruded out of the joint where the screw compresses it. I specifically said to avoid being under a screw head but in a lug where you have a set screw, I can't imagine a scenario where there would much lead in the joint to "creep". A twisted joint will have significant copper to copper contact and the solder will only be filling the gaps. (We all DO know we solder AFTER we make the physical connection ... right?) Where the screw contacts it, the solder would be pushed out of the way, making a copper to screw joint. Where is the "creep" going to be?

If you look at the utilities who supply it you will see 2 phase is a subset of

3p wye. You will also se the 120/240 is sold as "single phase" and most of these utilities will not supply 120v (what these folks here are calling single phase) Try

I read in sci.engr.electrical.compliance that s wrote (in ) about '30A wiring advice - a complication?', on Wed, 1 Oct 2003:

If you look at it like that, you get the confusion that troubled the OP. You have chosen the explanation of the centre-tap to 'prove' your assertion. But one 120 V supply behaves exactly as a single-phase supply, and so does the other. When you look at the two together, the important phase-difference comes into consideration. Your explanation 'hides' the phase-difference.

Yes, you are missing something. A two-phase system does not create a rotating magnetic field, as a 3- or higher- phase system can do. So the motor won't start. The starting capacitor and the second winding DO create a rotating field.

A 'two-phase' system with 90 degrees between the legs (which is really half a 4-phase system - the angles must add up to 360 degrees) would create a rotating field, but it is not easy to derive such a supply from the public electricity system.

Many of us Americans are indeed ethno-centric, not realizing what the standards are or differences in other parts of the word...

However, not all of us are like that and some of us even know that the AWG stands for American Wire Gauge, and perhaps this might not be the standard in use for European countries. And some of us do indeed understand that CH is geographically within the EU (mostly) except that sometimes a CH is actually an LI.

Beachcomber

It MUST be two phase between the two hot wires, because if it was in one (the same) phase then the heating element would not heat up.

- +ve 120V - - - - - - - - - -ve 120V

+

- +ve 120V - - - - - - - - - -ve 120V

= no potential difference between the two hot wires and so no current flow. Waves are in a single common phase.

- +ve 120V - - - - - - - - - - - - -ve 120V

+

- +ve 120V - - - - - - - - - - - - - - -ve 120V

= 180 deg phase shift, 240V potential difference at peaks therefore current flows therefore heater heats up.

In terms of maths/physics/engineering you are clearly correct.

In terms of the US electricity supply industry, "2-phase" is a specific jargon term which applies to only one 2-phase system. In the UK electricity supply industry, the common US scheme was called 2-phase (but is long obsolete and was never common).

Not really. Many of us claim that two linearly dependent voltages don't represent two distinct "phases", even if one of the proportionalities happens to be -1. John disagrees.

A two phase supply with conventional 90° (or anything != n * 180°, n is an integer) difference between the phases could be used in motors, as your comments suggest, or converted by a Scott-T transformer to make three-phase (or other polyphase) power. Canadian/US residential power cannot, so those who want to bring an industrial machine tool into their basement or garage have to use a static, rotary or VFD phase converter.

This has been discussed before...

Best regards, Spehro Pefhany

It would seem obvious that I knew that already. Why else would my reply state "Damned difficult to believe that 10-gauge wire is unavailable in Switzerland."