Temp power safety concern

[Lardog]

There is fire/flood repair contractor in our area that is using temp power as follows: he plugs a 3 wire cord into a 220volt dryer receptacle and then plugs in a temp power (spyder box) that has 20amp 120volt GFI receptacles; is this a legal and approved method of getting temp power for lights, drills, dehumidifiers etc? The cord feeding the temp power box is only 3 wire (2 hots and a ground) and the temp box is 4 wire (2 hots, 1 neutral, 1 ground), they are using the ground as a neutral to the temp power box. What safety concerns does this pose?

Thank you,
Lardog

 

[chris kennedy]

and then plugs in a temp power (spyder box) that has 20amp 120volt GFI receptacles

What is a spyder box? If this box doesn't have OCP devices for the recs. it would a violation of 590.4(C).

 

[mdshunk]

I'd try to worry less about what other contractors are or might be doing, and focus my efforts on those under my control.

 

[wbalsam1]

What is a spyder box? If this box doesn't have OCP devices for the recs. it would a violation of 590.4(C).

I agree. Poster should mention it (this condition) to someone in charge. Temporary power is often dangerous enough when one considers abbreviated wiring methods and/or hostile environments and the increased likelyhood of mishap.

 

[celtic]

What is a spyder box? If this box doesn't have OCP devices for the recs. it would a violation of 590.4(C).

This is a spider box:

Accompaning story:

NEC & OSHA: Protecting Workers from Electrical Shock

An exploration of both the NEC and OSHA's electrical protection requirements as it relates to GFCI protection for temporary wiring as required by Article 305 of the NEC and OSHA's 1926, Subpart K, Electrical Standards.
by Mike Callanan

From Dec. 2000 IAEI magaizine.



This is another style:

Temp Power Box Cat #52211 also known as a Spider Box. It features a common 50 Amp CS-Style (Construction Site) inlet and outlet for daisy-chain capability as well as 6-20 Amp 125 Volt U-Grd (T/L available) receptacles and 1-30 Amp 230 Volt L6-30 T/L receptacle, all GFI C/B protected.

http://tempower.net/_wsn/page3.html

 

[zbang]

What is a spyder box? If this box doesn't have OCP devices for the recs. it would a violation of 590.4(C).

The classic spider box contains 6 20a 1p breakers and has a 2p 60a (L-L-N-G) input, usually using an "RV" connector. The boxes are fairly common, but really need a four wire connection.

 

[dbuckley]

These boxes wired this way as potentially lethal. I've seen something similar to this in the UK (but worse, without GFCIs) and I had a heck of a job to persuade the EC who hacked it up that it was unsafe. Do whatever it takes to get it fixed.

The problem is that if the ground of the dryer plug becomes unglued then you get the wild neutral thing, which is well understood, but the real danger is that that wild neutral is also the "ground" of everything plugged into that box, including the metalwork of all the tools plugged into the box. In the situation described there will probably be people holding those tools, and maybe they'll be knee-deep in water.

Maybe the GFCIs will open and save the day (assuming they are double pole), maybe they wont, or at least not immediately. GFCIs are designed to work from stable power, not power of unknown voltage with the wild neutral situation.

The NEC disallows this kind of malarkey with sub-panels, and for exactly this reason. Though somehow it's OK for dryers, which baffles me, the NEC code makers must have been on acid that weekend.

The better versions of these boxes have a transformer in them, and so have a locally derived ground at the box (SDS), at least meaning the workers with tools in hand don't get shocked.