70's Code question

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augie47

augie47

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State Electrical Inspector (Retired)
I inspected fire damage at a motel today. The existing wiring will probably be "grandfathered", but I wondered about legality at the time of installation. I'm told the motel was built in early 70's. The wiring method is open 500 kcmil feeders on insulators mounted to the ceilng joist (approx 15' AFF) in the ulity corridor. 100 a mp M/B panels are tapped off via conduit stubs. The n & g are mixed..neut from the open run. At a later date, a THHN coductor has been added to the N-g bar and connected to a 2" galv water line in the same corridor.
Some of you guys with OLD Codes, any idea if this was legal in the early 70's ??
 
Article 320 in the 1971 NEC is Open Wiring On Insulators. In the 2005 NEC it is article 398. In the 1971 NEC open wiring on insulators shall not be used (1) in commercial garages, (2) in theaters and assembly halls, (3) in motion-picture studios, (4) in hoistways, and (5) in hazadous location, except in storage comartments of Class III locations as provided in Section 503-3(b). The 1971 NEC was a lot less stringent than the 2005 NEC. Open wiring on insulators is only permitted for industrial or agricultural establisments in the 2005 NEC. As far as the grounding and taps I didn't look for that in the 1971 NEC.
 
Thank you so much.
Since power was ON, I assumed it passed inspection when built.
In that the "grounds" were added, i would appreciate your taking a glance at that if and when you have time.
Thanks again.
 
How long are the tap conductors? What size of conductor are they tapping off 500 KCM with? I couldn't see the picture. As far as the grounding if you could cite me a code section out of the 05 or 08 NEC I'll look and see if there is a section in the 71 NEC that would cross.
 
The taps are approx. 15 ft., #2 tapped off a 500 kcmil..400 amp protection. Not legal today where it is, but possibly o.k. then.
240.21(B)(4) would allow for industrial..same as open wiring now.

Th neutral-ground mix would be a violation of 250.24(A)(5) today.
If the water pipe was ever allowed for a ground, I would think it would be around 250.134-136, but anything is possible.
 
The 10 foot tap rule in the 1971 NEC 240-15 Exc No.5 did not have the 10 times ampacity of the tap conductor unlike 240.21 (B) (1) (4) in the 05 NEC other than that it's pretty close. The 25 foot tap rule in the 71 NEC does have the one-third ampacity rating in section 240-15 Exc No. 6. It looks like the taps were in violation when installed. I'll have to check into the grounding when I get a little time.
 
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