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#89001 - 08/21/04 11:17 AM Acceptable Ground Rod?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I went into a electric room and saw this cord, I know what it is for as each of this customers locations has one of these cords.

This cord is used to power a temporary refrigerated trailer, each loading dock has an outlet to plug these into. When the trailer arrives the cord gets hardwired to the refrigeration unit.

Someone apparently decided that this trailer needed a ground rod.

So some questions.

Do you think this application requires a ground rod?

Do you think this ground rod is acceptable?

I already have my own opinion I am hoping to cause some discussion of the various code articles that may or may not apply.



Bob



_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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2014 / 2011 NEC & Related Books and Study Guides
#89002 - 08/21/04 11:28 AM Re: Acceptable Ground Rod?
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
Bob,
In a previous life did it used to be a lightning air terminal?
No need for the rod at the trailer.
_________________________
Ron

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#89003 - 08/21/04 12:07 PM Re: Acceptable Ground Rod?
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
As Don (resqcapt19) has astutely pointed out in posts at E-C.net, a very [perhaps the most] critical part of “grounding” is bonding to limit potential difference between equipment enclosures/components. This is only achieved through low-impedance interconnections, where relying on ground electrodes to establish any sort of return path for <600V systems is nothing short of treacherous. Applied to portable equipment, driven rods can give a false sense of security that local electrical things are “safe,” sometimes to the point of little concern for properly installed, low-impedance bonding routed with circuit conductors.

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#89004 - 08/21/04 12:23 PM Re: Acceptable Ground Rod?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Some info I should have provided.

This is a 208 or 230 volt (depends if buck boosts have been installed) straight 3 phase feed with ground.

The outlet / plug combo is rated as a disconnecting means.

The breaker inside is a standard 3 pole 50 amp.

Another question, does the white need to be re-identified as it is used as an ungrounded conductor?

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#89005 - 08/21/04 01:08 PM Re: Acceptable Ground Rod?
capt al Offline
Member

Registered: 06/20/04
Posts: 203
Loc: Norton, Ma USA
Bob, I hope the maintenance dude that did this did not tap into the Meltric connector. What kind of ground resistance is a foot long rod going to provide?

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#89006 - 08/21/04 06:39 PM Re: Acceptable Ground Rod?
hbiss Offline
Member

Registered: 12/16/03
Posts: 893
Loc: Hawthorne, NY USA
I would say that the white cannot be use as a hot phase leg. Not sure if it is legal with flexible cord to re-identify it though. Might have to use 5 wire SO cable.

You say that it is fed from a 50A breaker. That doesn't look like #6 to me and is the plug/receptacle rated at 50A?

That cut off ground rod is a joke. A ground rod is not needed anyway.

-Hal
_________________________
www.myphonetechs.com

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#89007 - 08/21/04 07:49 PM Re: Acceptable Ground Rod?
dansan Offline
Junior Member

Registered: 08/05/04
Posts: 5
Loc: Murfreesboro TN USA
White wire in cable assy. ok to be used as ungrounded conductor if permanently reidentified. 200.7(C)(1) Never have seen any provisions for a 1' supplemental electrode though.

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#89008 - 08/22/04 05:13 AM Re: Acceptable Ground Rod?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Here is what I think is interesting.

200.7(C)(1) refers to cable Assemblies, that would be NM, MC, BX, SE etc. I am not sure that flexible cords and cables fall under that category.

Notice a separate section in 200.7(C).

200.7(C)(3)Where a flexible cord,.....

They made a separate section for cords and no mention of re-identifying the white when used as an ungrounded conductor.

What is up with the separate section if flexible cords are 'cables'?

Confused.

Article 400 calls some cord and others cable, what determines a cable from a cord?


Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#89009 - 08/22/04 05:18 AM Re: Acceptable Ground Rod?
PCBelarge Offline
Member

Registered: 06/08/03
Posts: 657
Loc: Dobbs Ferry, NY, USA
225.30 tells us that a multiwire branch circuit can be considered as 'a' branch circuit, and a disconnect is not required.

Structure- That which is built or constructed.


250.32(A) says that at each building or structure (trailer) that one or more feeders or branch circuits requires us to follow part III of 250. (paraphrased to shorten this post)

550.4(A)Mobile Homes Not Intended as a Dwelling Unit.
-for example, contractor's on-site offices,...
...shall meet all other applicable requirementsof this article if provided with an electrical installation intended to be energized from a 120v or 120/240v ac power supply system.

I can see that your in your post this is a refridgerated trailer, but I am interested in 'job' trailers as well

After reading all of these articles, it would seem they contridict each other.
Bottom line, I am still confused.

would a 'job' trailer with a 'single' branch circuit (whether from 3phase or single phase) require a ground rod?

I do understand the principle behind the reason for the installation of ground rods.

Pierre
_________________________
Pierre Belarge

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#89010 - 08/22/04 06:07 AM Re: Acceptable Ground Rod?
cpal Offline
Member

Registered: 05/17/04
Posts: 165
Loc: Cohasset MA
Iwire

I was told that the term cable is applied to factory assembled cables such as NM, MC, etc. as well as single insulated conductors made of standard stranding. I was also informed through proposal process that the NEC does not define standard terms. It appears that a dictonary will define a cable (electricaly) as heavey strands, and it will also define cords as small or thin strands and being fitted with a plug or plugs.

Still not concise but it moves in a direction

charlie

[This message has been edited by cpal (edited 08-22-2004).]

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