Subpanel, when is or when it isn't

[Woodway]

Question from another forum and now it's got me interested. One of the posters has a home under construction with temp power pole in yard. The service at the pole is tied to combination panel (panel with meter and breakers). He didn't say but I assume that the pole is bonded to ground rod. The panel has 200 amp disconnect with "feed through lugs" at the bottom of each buss bar. The guy get OK from local inspector on pole install and 100 amp single phase feed from pole combo panel to an on site trailer. Then he runs a three wire cable (two phase wires and neutral) from the "feed through lugs" to the main panel in the house by using a trench between the two. The panel in the house is bonded to a second ground rod system and has it's own disconnect . He gets two answers from two inspectors on the cable in the trench. One inspector ok's the three wire cable while a second inspector says that before he can give the OK he, the building owner, must first install a four wire cable in the trench and not tie the neutral and equipment grounds together at the house panel. What is correct here? Article 250-32(b)(2) was my choice as the controlling article for this setup. Was I correct there was no continuous metallic path between the grounding system at the pole and at the house (ie. No equipment ground was installed in the trench between the house and the pole, only the neutral wire was installed with the two hots) Note, at the house the neutral from the three wire cable was bonded to the panel and ground rod system of the house and the house panel has it's own disconnecting means.

I'm always open to new ideas and correcting those that I have wrong . Great forum for learning and expanding electrical code background.

 

[bdarnell]

I agree with the first inspector and your interpretation of 250.32(B)(2). The three wire cable should be permissible with a N-G bond at the remote panel.

 

[George Stolz]

Agreed.

 

[pierre]

I do not like this rule in 250, but this may be a very good example of why it is permissible.

I can see this as a fine installation, as it is temporary and the chances of a metallic path installed between the two is not likely.

 

[tom baker]

In Washington State we can not reground the neutral.
I suspect the NEC will do away with 250.32 in 2008

 

[don_resqcapt19]

Tom,

I suspect the NEC will do away with 250.32 in 2008

My comment will be "we can do that only after we do away with 3 wire services".
Don

 

[pierre]

I think Ryan posted that the proposal to do away with this type of installation was rejected.

 

[romeo]

There is no need for egc and the neutral can be bonded to the panel enclosure if all the requierments of 250.32(B) (2) are meet.

romeo

 

[engy]

Wouldn't article 550 require the magic 4th wire?

 

[benaround]

I agree with engy, this feeder is going to a moble home. 550.16(B)

 

[iwire]

No one has said this is, or ever was a mobile home.

The OP stated on site trailer, I take that to mean a 'job trailer'

550 will not apply

 

[eprice]

I agree with iwire but add that the OP is asking about the feeder between the pole and the house. He has not even told us how many conductors are in the feeder to the on site trailer.

 

[chiefrider007]

The more I look into the 3-wire vs. 4-wire feeder systrems, the more I just don't understand. I can not see the difference, (electrically speaking) between the two. It seems to me that it shouldn't matter what type of home a person has, one way or the other, and if there was only one correct way, we all wouldn't have all this confusion.
If no EGC is used, neutral grounded at meter then bonded at home panel, there is still a ground path, right?
My home was placed on site, yes it is one, last October and I used a 3-wire feeder, which was what my power company suggested. The feeder was ran before the home was delivered. I've posted here before on this matter.
Anyway, power problems, lights blink when furnace, a/c, hot water, even the frig when they first start. Also checked recently and ckt. bkr. for hot water heater is warm on the back of my hand after I take a shower.
Company I bought home from says that I will have to either hire an Electrician or find a problem in the home myself before they will cover the wiring, (inside the home) under the warranty. I can understand the fact that they don't want to spend the money to check all electrical connections in my home and make it right but really.
Maybe my best option would be to either run a 4-wire feeder or repair connections. What do you think would be best?

 

[suemarkp]

The difference is, when there is no separate EGC, there will be a voltage difference between each end of the feeder neutral if any current is flowing in the neutral (equal to the voltage drop in that wire). This voltage difference will allow current to flow from one electrode to all the others in the neighborhood because this conductor is grounded.

With a separate EGC, the only time you should be getting current through the earth is during fault conditions.

To make this really effective, the power company would need to change the way they distribute power to each service and run a separate EGC there too. Otherwise, you're still going to have currents in the earth between the first service and the supplying transformer. And after all of this, there will still be voltage differences between adjacent power poles and since each tranformer is grounded there will be current flow between the poles. But you could argue that this is much better than what we have now with many house feeders and services dumping current into the earth.

 

[chiefrider007]

Thank you, I understand what you are saying. What good does the EGC do with the meter base grounded/bonded to neutral by the POCO already anyway?

 

[chiefrider007]

Sorry but a couple of other things. Since the meter is grounded/bonded, wouldn't it just go to ground there, the same as it would if bonded at the house?
If POCO removed their bond at the meter it would still be at the transformer, right?
I'm leaning toward just pulling a new feeder. My current 3-wire is made to be burried but inside 2" PVC for protection. I should be able to pull it out and the new in at the same time, I think/hope.
Thanks everyone for your replies.

 

[engy]

"No one has said this is, or ever was a mobile home.
The OP stated on site trailer, I take that to mean a 'job trailer'
550 will not apply"

Read the poor wording in 550.4
Mobile Home not intended as dwelling unit...classic

Job Trailer = Contractor On-Site Offices?

I've seen the wind blow both directions on this issue.

 

[ryan_618]

I think Ryan posted that the proposal to do away with this type of installation was rejected.

No, quite the opposite actually. At the straw vote, it was accepted, although not unanimously.

 

[engy]

Point of clarification, for me, if no one else...

The 3-wire feed to the house would be OK, which is what the OP is concerned about.

The trailer would need 4-wire per 550