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New Subpanel/Load Center, Old Feeder


Rob Amaral
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Perhaps someone can tell me 'why' this is 'no-noguchi'"

Circa 1958 'service' in multi unit bldg (about 15 units). Bldg disconnect ahead of multiple meters, each feeds a 60A disconnect that has an old 'feeder' (2 hots/1 uninsulated neutral) to the in-unit subpanel load center.

One apt (now condo) gets gutted and rehabbed totally and gets all new NM-B, new subpanel load center.

Electrician still keeps old feeder, unbonds neutral bus (floating), 'bonds' the equipment ground bus to the enclosure and runs a grounding wire (insulated jacket) to a water pipe below the apartment that is supposed to act as a 'return path' for any ground fault current.

I basically said it is improper for a couple of reasons (ground wire needs to be in the same 'jacket' as the 2 hots and the neutral and that water pipes are not supposed to be used as an 'intended' path, even in a ground fault situation).

Doo-doo is flying because it is the 11th hour of the transaction and I'm trying to find that 'reason' for the wire to be in the same sheath (as in new feeders). I know its one of the "Electrical vood-doo" reasons that we don't bring up often but I cannot remember why.

While I look today, any of you guys know 'why' this is wrong?

I told them that optimally, a new feeder should be run and that in the meantime, it might be better to ask the city inspector if it is ok to have the neutral bonded to the enclosure like all the other apt units still do at this time rather than use plumbing as a deliberate "intended ground fault path".

I said what the guy did here is backwards thinking and that the only time you connect pipes to the ground system is for grounding electrode and to 'bond' the pipes ('catch' stray juice). It would be nuts to 'send the juice there' in order to try and clear a ground fault. The bldg is circa 1910. I figure there is cheesy threaded brass pipes anyway.

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Originally posted by hausdok

Once again, I quote from Douglas' book, Electrical Inspection of Existing Dwellings. (You know, you really should get this book. It'll save you a lot of aggravation.)

I recieved that book among other materials at basic training, and I also highly recommend it, particularly for newbies. Like everything I've read by Douglas, it's clear, sensible, and to the point. [:-thumbu]

Brian G.

Reading Is Fun-damental [:-glasses]

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Boyz: Tnx. I have that book (stuffed in the shelf!). I'll get it out. A great book by the way, Doug. I had no time this AM to check this stuff out. Hit the road before 6 to get into Boston and we were getting hit by an 'ice storm' in the morning. Interesting few hours this morning (travel-wise).

Much appreciated!

R

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BTW, another book I gleaned a lot from is "Soares Book on Grounding" (I think). I got a lot out of it. Another book I have that is pretty interesting is "Electric Railways" (I forget by who) but it shows you how to wire a house with knob and tube. Awesome illustrations and very detailed explanations.

On another note, a dog got electrocuted here in Boston in the past week while its owner was walking it on a public sidewalk. The papers screwed up the details but I see a lot of super-corroded underground laterals in Boston and I'm not suprised.

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Mike:

Awesome that you would even attempt to post what you did here for me. God bless you. I do have this book and I'm on the way... Thanks for even spending to time to find the book on the shelf. Like a lot of inspectors, I bought a ton of stuff over the years and only seem to go back to a few things once in a blue moon. Once I initially read this stuff, I tend to 'stash' it unless I really need to find it.

To be honest, the most common thing I look up is the clearance from a fireplace mantel to the fireplace opening... for some damn reason, I just can't remember it.

I found this book and see I've even spent time highlighting it. You'd think I'd remember even owning it. Too busy (which is good but which is also bad).

I told my client last night (this was at 630P and 'onsite') that I'd post this on a forum and that I knew I'd get some responses and that an electrical expert in CA (who is probably not an electrician, correct?) would know or someone would post something.

Thanks again and thank you Mr.Hansen, you 'done good'.

Rob Amaral

Walpole, MA

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I dug up 'why' this subpanel feeder issue I found was wrong. Running a separate equipment ground wire conductor that is not in the same cable as the feeder circuit conductors is improper because it can increase the impedance of the ground fault current and cause the overcurrent device to not trip in the proper amount of time. Has to do with magnetic flux, cancellation, proximity of conductors and a bunch of other voo-doo.

I always like to know 'why' something is wrong rather than 'because they say so" types of answers. Shoot the 'why' to the guy who fouled up and you can watch the face blanching... Not fun but necessary.

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