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What is considered a high neutral current?

What is considered a high neutral current?

What is considered a high neutral current?

(OP)
Just curious. I was reading a load report that stated there was a high neutral current on a 200A Main Breaker in a 120/208V panel. The current on the breaker was 33.6 Amps. Is that considered too high?
Thanks,
-Mike

RE: What is considered a high neutral current?

If you have 33.6A of single phase or unbalanced load then NO.

What is the load in each phase?

RE: What is considered a high neutral current?

What do you mean by "current on the breaker"?  The neutral normally has no breaker.
 

RE: What is considered a high neutral current?

oh..good catch jghrist. I should have read it more carefully. I assumed he is talking about 33.6A of neutral current.

selfentitled:
You need to clarify the questions above.

RE: What is considered a high neutral current?

(OP)
Current on the Neutral in the panel, correct.  No neutral breaker :).  The breaker is about 150A / phase loaded.  

I can see 33A on a neutral being an issue, but how much is too much?

RE: What is considered a high neutral current?

Usually, no unless you have a reason to believe it should not be there. Check it against the expected unbalance and harmonics.  

RE: What is considered a high neutral current?

Why would it be an issue? Seems pretty reasonable to me.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: What is considered a high neutral current?

If the neutral currents sum to equal the neutral currents, then there is no problem having a neutral current. It can be a problem if the sum of the phase currents doesn't equal the neutral current.

A difference can indicate a problem usually in another circuit.

This means that you may be getting some current flowing up in your neutral from someone else's, which is trying to get back to the transformer.

Ausphil

RE: What is considered a high neutral current?

What type of loads are connected to this panel?

RE: What is considered a high neutral current?

Do a vector sketch of the phase currents. If the neutral current is more than indicated by the vector sketch, you probably have third harmonics.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: What is considered a high neutral current?

(OP)
Must be harmonics.  
Phase A: 145A
Phase B: 143A
Phase C: 158A

Neutral Current = √((Ia²+Ib²+Ic²)-(Ia*Ib)-(Ib*Ic)-(Ia*Ic))
= √((145²+143²+158²)-(145*143)-(143*158)-(145*158))
= 14A

This is all great input, thanks!

RE: What is considered a high neutral current?

What size is the neutral conductor?  Harmonics or not, I don't see a real issue until the neutral load gets close to the ampacity of the conductor.  On a 200 amp circuit it is very common to have the neutral conductor with the same ampacity as the ungrounded conductors.  If that is the case I would not worry about the neutral current unless it was well over 100 amps, unless you think the source is other than harmonics.  Now that is not to say that the harmonics are not causing other issues that need to be addressed.

RE: What is considered a high neutral current?

I think we cannot give general rules.Recently I saw 10 % of phase current as neutral current in a 100  MVA 132 kV generator transformer.After a lot of investigations it was found  out that one  of the phases was having  one tap less voltage( ie 1.25 %) due to a defect in tap changer coupling.Once rectified neutral current came down to nil.
In power stations a small neutral current in generator transformers is common to the extent of 5-100 A.

In low voltage distribution lines considerable neutral current can come with unbalanced loading. This may some times  exceed phase current, when the load generates a lot of third harmonic  currents in addition to unbalance loads..

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