Daisy-Chaining 480v Cords

[ERP]

Hi:

I have been coming to Mike Holt?s website and occasionally lurking here when I have an electrical question and have always readily been able to find my answers, but now I am into some stuff where Google and lurking are not going to answer my questions!

We have just begun running a 480v 3 phase generator on a trailer, then main power cables to a distribution box, which then is distributed to power multiple 460v heaters at industrial jobsites.

As using this type of equipment and working with this kind of voltage is new for our firm, I have a host of questions.

First Question: The main power cords are either 50 or 75 foot lengths of Carol 6/4 600VAC with Hubbell 50amp ends. (Photos below) The challenge is we are frequently running these a lot further than 75 feet, so the manufacturer tells us to daisy chain these together! I have always understood daisy-chaining was a no-no, but they say this is fine up to 800 feet with these cords (daisy-chaining up to 16 cords!) From a pure safety standpoint my biggest concern is with these cords being disconnected or re-connected with a 480V load on them. So is this legal and safe or not?


Second Question: I am being further told we are to run these up the sides of buildings daisy-chained. Even with some safety straps I cannot see how this can be safe or legal!

I have more questions, but I figure I will leave it at these two for this first post!

Thanks!

Eric

 

[xformer]

Look at 400.7 and 400.8 in the 2008 NEC.

IMHO I don't see where this would be allowed.

 

[ERP]

Look at 400.7 and 400.8 in the 2008 NEC.

IMHO I don't see where this would be allowed.

Hmm - I had already looked at 400.7 and 400.8 and I don't see what in those sections provides clarification for my questions:

400.7 Uses Permitted.
(A) Uses. Flexible cords and cables shall be used only for the following:
(1) Pendants
(2) Wiring of luminaires
(3) Connection of portable luminaires, portable and mobile signs, or appliances
(4) Elevator cables
(5) Wiring of cranes and hoists
(6) Connection of utilization equipment to facilitate frequent interchange
(7) Prevention of the transmission of noise or vibration
(8) Appliances where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance and repair, and the appliance is intended or identified for flexible cord connection
(9) Connection of moving parts
(10) Where specifically permitted elsewhere in this Code
(B) Attachment Plugs. Where used as permitted in 400.7(A)(3), (A)(6), and (A)(8), each flexible cord shall be equipped with an attachment plug and shall be energized from a receptacle outlet.
Exception: As permitted in 368.56.

400.8 Uses Not Permitted. Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following:
(1) As a substitute for the fixed wiring of a structure
(2) Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors
(3) Where run through doorways, windows, or similar openings
(4) Where attached to building surfaces Exception to (4): Flexible cord and cable shall be permitted
to be attached to building surfaces in accordance with the provisions of 368.56(B)
(5) Where concealed by walls, floors, or ceilings or located above suspended or dropped ceilings
(6) Where installed in raceways, except as otherwise permitted in this Code
(7) Where subject to physical damage

 

[zbang]

I don't see where using multiple lengths of cord would be prohibited where a single one is permitted, at least I've never see a citation for this (not in 400, 523, 525, or 590). It's certainly common practice for temporary power and pretty much required in some places (say, generator on street to switchboard in basement for a planned outage).

Your concern about hot-plugging is good, I don't like it at 120/208, much less at 277/480. If you can't be sure of the load about to be connected, lock out the feed, then connect. And check the spec sheet for the connectors, they'll tell you whether they're rated for load interruption or not (and I very much doubt they are).

Also, take a look at 590, where you see things like 590.4 (H) "Protection from Accidental Damage. Flexible cords and cables shall be protected from accidental damage." or (J) "Support. Cable assemblies and flexible cords and cables shall be supported in place at intervals that ensure that they will be protected from physical damage." In theory, you could run the 6/4 up the outside of a building, as long as you properly support it.

 

[Rick Christopherson]

I have (past tense) been associate with portable power distribution for around 30 years (I started young), and what your manufacturer is telling you is correct and standard practice. Daisy chaining the cables is normal and permitted. You could request longer cables be made, but they really become a bear to handle longer that 75 feet. That's why 50 foot is the common length...75 is a bit of an exception.

When you are dealing with really long lengths, it is more desired to keep your distribution panel as close to the load as possible, so you are feeding your greatest length with the 2/0 or 4/0 feeder, and minimizing your length of the smaller #6-4 branch.

As for going up the side of a building, that really depends on the height you are suggesting. It can be done, but may require support of the cable. A single story rise is not a problem for that cable, even with a joint in the middle. Anything beyond that and you need support the cable so it is not taking the full load of its weight. That is true for any portable cable type.

 

[btharmy]

For temp power, I don't see a problem with daisy chaining cables from the generator to the load. Ever try to carry a 100' 6/4 s.o. cord. No way.

As far as connecting/disconnecting the cord caps under load. I would not do it on a 208v system, let alone a 480v. I don't see why it would be necessary to connect or disconnect under load. It just seems dangerous to me.

 

[mtenerowicz]

Disconnecting

Disconnecting

I believe 70E has issues with disconnecting live loads without proper hazard analysis. 70 art. 430.1 has issues with disconnecting motors under load. Also I don't have all the code references right now but I think any device that will be interrupting loads must have an SCCR on it. Try using something like the Meltric (www.meltric.com) connectors if you plan on doing this.

 

[ERP]

Thanks all -very helpful!

For temp power, I don't see a problem with daisy chaining cables from the generator to the load. Ever try to carry a 100' 6/4 s.o. cord. No way.

As far as connecting/disconnecting the cord caps under load. I would not do it on a 208v system, let alone a 480v. I don't see why it would be necessary to connect or disconnect under load. It just seems dangerous to me.

I am not suggesting that it be done; I am however suggesting that this is a likely foreseeable outcome of daisy-chaining cords, that at some point someone will indeed separate the cords while under load with possible disastrous outcome.