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Acceptable Ground Rod? #89001
08/21/04 01:17 PM
08/21/04 01:17 PM
I
iwire  Offline OP
Moderator
Joined: Jan 2003
Posts: 4,391
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.

[Linked Image]

Bob

[Linked Image]

[Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
2017 / 2014 NEC & Related Books and Study Guides
Re: Acceptable Ground Rod? #89002
08/21/04 01:28 PM
08/21/04 01:28 PM
R
Ron  Offline
Member
Joined: Mar 2002
Posts: 582
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
Re: Acceptable Ground Rod? #89003
08/21/04 02:07 PM
08/21/04 02:07 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
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.

Re: Acceptable Ground Rod? #89004
08/21/04 02:23 PM
08/21/04 02:23 PM
I
iwire  Offline OP
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Acceptable Ground Rod? #89005
08/21/04 03:08 PM
08/21/04 03:08 PM
C
capt al  Offline
Member
Joined: Jun 2004
Posts: 206
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?

Re: Acceptable Ground Rod? #89006
08/21/04 08:39 PM
08/21/04 08:39 PM
H
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
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

Re: Acceptable Ground Rod? #89007
08/21/04 09:49 PM
08/21/04 09:49 PM
D
dansan  Offline
Junior Member
Joined: Aug 2004
Posts: 5
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.

Re: Acceptable Ground Rod? #89008
08/22/04 07:13 AM
08/22/04 07:13 AM
I
iwire  Offline OP
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Acceptable Ground Rod? #89009
08/22/04 07:18 AM
08/22/04 07:18 AM
P
PCBelarge  Offline
Member
Joined: Jun 2003
Posts: 681
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 [Linked Image]

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
Re: Acceptable Ground Rod? #89010
08/22/04 08:07 AM
08/22/04 08:07 AM
C
cpal  Offline
Member
Joined: May 2004
Posts: 162
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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