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Help! #46930 01/05/05 11:57 PM
Joined: Nov 2004
Posts: 3
A
AinSophAur Offline OP
Junior Member
This is a real head scratcher. There is 400 Amp service drop. From the lugs of of the meter, there are two sets of feeders (for two seperate 200 amp services)paralleled from the same lugs each going directly into a 2" underground run. One goes directly in to the house panel. The other goes to the back house/shop. It has operated fine for years. I come out on a service call, the power just died at the back house. It turns out that one phase is dead from the meter to the panel. At the meter lugs I have 120 to ground on each phase and 240 between them. At the panel (only 50' away) I have 120 to ground on A phase, nothing between B and ground and 120 between A & B. There are no breakers tripped and nothing between the meter and the panel, but still I have voltage on one end of B phase and nothing on the other. I feel like there must be something I am missing but I just stood there dumbfounded.

Work Gear for Electricians and the Trades
Re: Help! #46931 01/06/05 05:57 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
"I have 120 to ground on A phase, nothing between B and ground and 120 between A & B. "

You may be measuring through the connected load on B through to the neutral? (poss phase loss on B)

Are you using a DMM, a solonoid, or neon tester? Solonoid or neon, and your probhably getting 90 - 160V, and it may look like 120V between A + B. (poss phase loss on B, or lost neutral)

Any recent gardening?
Corrosion?
Bad CB?
ETC.......

Anyway, it's a possible high low voltage hazard, hope you didn't leave it connected in this condition?


Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Help! #46932 01/06/05 09:34 AM
Joined: Aug 2001
Posts: 329
S
Steve Miller Offline
Member
I wouldn't do too much gardening barefoot out there. Sounds like B burned in half & is in contact with ground. Try an amprobe on B at the meter & see how much is leaking. Might also want to disconnect B at the meter to prevent a voltage being injected in the ground. Sounds like the real problem here is how to dig it up and replace the pipe & wires to the shed.

Re: Help! #46933 01/06/05 02:53 PM
Joined: Nov 2004
Posts: 3
A
AinSophAur Offline OP
Junior Member
I used a Digital meter and there is no current on either end. It just seems unbelievable to me that one phase in a conduit could completely be severed and not touching itself at all and the rest remain in tact,. At the time I didn't have much time to do any more investigation, but will return.
Thanks

Re: Help! #46934 01/06/05 06:11 PM
Joined: Apr 2004
Posts: 42
S
sparkystudent Offline
Member
quote
It just seems unbelievable to me that one phase in a conduit could completely be severed and not touching itself at all and the rest remain in tact,
if it is in pipe (conduit) is the run solid and continueous if there is an open place and isnt in pipe gophers can chew on just one wire and it will corrode and then when it is corroded far enough it falls apart and seperates i replace about 10 - 12 a summer here where im from usually in sandy soils where gophers moles and ground hogs are prevalent BTW does anyone know the reason they (rodents) chew wire insulation. have been told it is the vegetable oil used to make the jacket. nice job security [Linked Image]

Re: Help! #46935 01/06/05 11:19 PM
Joined: Aug 2004
Posts: 34
H
highkvoltage Offline
Member
sparkystydent. It happens all the time.

I also believe you have lost phase B and that you are get a reading from a 220 load. I would use a Megger and test the conductors. You may find out that phase A and/or the neutral is also damaged.

Re: Help! #46936 01/08/05 01:58 AM
Joined: Nov 2004
Posts: 9
B
beaman Offline
Junior Member
If phase A was tested against ground, at 120, AND, 120 to phase B, how could a 220 load create potential into phase B, since the potential in phase B is from phase A?

I know that this doesn't answer the problem, since phase B reads no potential to ground also, which it would from the phase A feed if it were through a 220 load.

Brad

Re: Help! #46937 01/08/05 04:45 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
I think these voltage readings are off in some way, for some reason....

The measurement to the B phase, is off. It has to be either slightly, or a lot off, on one, or the other. (A - B, B - N) Knowing which one, is key to knowing more about this problem. So is knowing the conditions when it was measured. (Under load or not.) Not to mention what they were measured with, a good DMM, or a wiggy. (The latter being a burden to the situation, due to false readings.)And in your last post you say DMM, it still sounds fishy to me.

Knowing the correct (more exact) readings will probhably give you one of two scenarios.

Full or partial Neutral loss.
Measured under load would be simular to this.... Depending on the amount of load on each phase, as they would be totally or partialy in series through the connected neutral within the building. A - N above or below 120, B - N >0-120, A - B 120-<240.

Or the suspect loss of B phase.
Also measured with the connected load of the building would explain the supposed 120 at A - B, as you'll be measuring through the load of B to N.

There is also a set of measurements missing from the mystery, A,B,N to Ground? Were you measuring to ground, or grounded conductor (Neutral). This building should have one of both. Often the best, if not the best place to refferance voltage from ground. I would be interested in the reading between these two. And measuring with no load, vs with load, although the latter isn't hip as it could damage something if it's a neatral problem.

Regardless, it sounds like a job for a shovel.

As for rodents and insulation, they use it to insulate thier nests and hollows. I have spotted nests made of Romex jackets before, and once, a long dead rat who died in the act. (Dead Short)


[This message has been edited by e57 (edited 01-08-2005).]


Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Help! #46938 01/08/05 03:02 PM
Joined: Nov 2004
Posts: 9
B
beaman Offline
Junior Member
I have seen corrosion built up on a breaker lug that insulated the wire from carrying current. I tested for power at the breaker by touching the test probe to the screw of the breaker lug, got a reading and went about testing further only to be "dumbfounded". After a while, I found that the wire at the breaker tested zero when I stuck the probe through the insulation, which caused me to look closer. Also, a break in al. wire can be invisible to the eye.

brad


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