Parralell Circuits

[michael nye]

Re: Parralell Circuits

No I am not putting you on this is a real situation in a real house, I just wanted to break this down and see what everyone thought. This site is not only informative but alot of fun. Thanks bennie

 

[bennie]

Re: Parralell Circuits

Michael: I guess you are serious. So here goes.

Conductors smaller than 1/0 have never been, and never will be approved, for parallel operation, except when overcurrent device is no larger than the ampacity of a single conductor.

This installation is dangerous, and will eventually fail. The insulation is 60?C. rated.

I don't know the details of your inspection, but if it involves the sale of this property, you as a public official, are required to make this code violation known and a matter of public record.

Installations, in violation of the code at time of original construction are never approved, no matter how much time lapses.

 

[michael nye]

Re: Parralell Circuits

Bennie what is a pundit, and thankyou for the info, I will mandate the updating of the work being performed.

 

[bennie]

Re: Parralell Circuits

Michael: Type in "Dictionary" and hit the go button on your browser. Word meanings are better understood when coming from a pundit.

 

[charlie]

Re: Parralell Circuits

I bet Charlie E hangs at their place too.

Roger, I have just gotten into this thread and was disappointed to miss out on the fun (I kinda pick and choose since I don't have enough time to do a lot). I appreciate being put into the same category as Bennie and Ed but I am not degreed. I have gotten my knowledge from experience and age. With that, I try to stay away from the areas I am not sure about.

I have worked as an engineer for 33 years, have about 10 years of electrical work (5 years as a Master Electrician and owner), taught 3rd year electrical apprentices for 8 years, and member of CMP-10 since 1994 (1996 cycle).

 

[iwire]

Re: Parralell Circuits

Originally posted by bennie:
Conductors smaller than 1/0 have never been, and never will be approved, for parallel operation, except when overcurrent device is no larger than the ampacity of a single conductor.

Bennie that is not true 2002 NEC 620.12(A)(1) allows parallel conductors as small as 20 AWG to add up to equal the ampacity of 14 AWG.

This installation is dangerous, and will eventually fail. The insulation is 60?C. rated.

At 60C 10 AWG is rated 30 amps you have two of them on a 40 amp breaker, can you explain why this is more dangerous than any house with old wire?

Installations, in violation of the code at time of original construction are never approved, no matter how much time lapses.

A great many houses have electric code violations but the code is not retroactive.

If this can be replaced great, but I am missing the urgency here, what makes conductors smaller than 1/0 dangerous in parallel?

 

[bennie]

Re: Parralell Circuits

Bob: Permitting #20 cu. to be in parallel to equal the ampacity of #14 cu. is because #20 cu. is all there is in the traveling cables for elevators. #14 is required for the lights. Instead of changing the cable, they changed the rules.

#10 cu is ten times the impedance of 1/0 on a per foot basis. A slight difference in impedance can have a large difference in current on #10. A slight difference in 1/0 will not be a big deal.

Corrosion on the #10's can effectively reduce the copper area to one conductor over a period of time. One conductor in an open state will cause overload on the remaining one.
For another occurrence...corrosion does not always increase impedance, it merely reduces the contact area and heat dissipating ability. Result is cooked terminals.

OK fellow students, jump in on this before I get into the Twilight Zone.

[ May 14, 2003, 05:44 PM: Message edited by: bennie ]

 

[iwire]

Re: Parralell Circuits

#10 cu is ten times the impedance of 1/0 on a per foot basis. A slight difference in impedance can have a large difference in current on #10. A slight difference in 1/0 will not be a big deal.

Thanks That makes sense, but why would one cable have a different impendence than the other? I am not trying to bust your chops I just do not understand.

My point with the elevator cables was that it must be a safe installation, or they would not allow it.

If using the 20 AWGs for 15 amp circuit was a safety issue the NECs answer would (or should) be get cables made with 14 AWGs in with the 20 AWGs or run a second cable with 14 AWG.

 

[bennie]

Re: Parralell Circuits

The #20 makes for redundant lighting conductors. One breaks, the lights still work. The connected load is not a large amount.

Wire and cable have different impedance due to many factors. A different factory run. A different length. Quality of terminals. Position in conduit.

[ May 14, 2003, 06:12 PM: Message edited by: bennie ]

 

[bennie]

Re: Parralell Circuits

Take a current reading on paralleled conductors, with a heavy load. The difference, in current, sometimes is quite a large amount. This will demonstrate the variation in impedance.

[ May 14, 2003, 06:17 PM: Message edited by: bennie ]

 

[noxx]

Re: Parralell Circuits

Nit picking -

In addition to other violations, the described circuit has to end in a breaker that has two wires under each lug. Since all lugs for the connection of more than one conductor must be identified as such (and I assume we all know your average forty amp CB is not such a device)the termination at the panel is also in violation.

-Noxx

 

[bennie]

Re: Parralell Circuits

I have seen newer houses destroyed by loss of one paralleled conductor. This automatically doubles the rating of the protective device for a single conductor.

One house fire was because the electric furnace was fed by two 50 amp circuits, the jumpers in the furnace were not removed making the feed parallel instead of separate. One breaker tripped forcing the entire load on the remaining circuit with a welded breaker. The No.#6 burned half way into the ceiling joist.

[ May 14, 2003, 09:24 PM: Message edited by: bennie ]

 

[Ed MacLaren]

Re: Parralell Circuits

Permitting #20 cu. to be in parallel to equal the ampacity of #14 cu. is because #20 cu. is all there is in the traveling cables for elevators.

True, and the reason is so the travelling cable will have the flexibility to withstand the bending that occurs each time the elevator moves up or down.

Also, the two or more #20s that are paralleled are not as likely to have different impedances, being part of a cable assembly, as opposed to being field installed.

Ed

 

[hurk27]

Re: Parralell Circuits

Noxx

and I assume we all know your average forty amp CB is not such a device)the termination at the panel is also in violation.

You might be superised how many breakers are listed for more than one wire, and we all know that Square D is, the ones that are not are fewer than the ones that are.
But this was a thread in the old forum.