What is considered a high neutral current?

[Selfentitled]

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

 

[rbulsara]

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

What is the load in each phase?

 

[jghrist]

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

 

[rbulsara]

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.

 

[Selfentitled]

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?

 

[rbulsara]

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

 

[alehman]

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

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

 

[ausphil]

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

 

[trosepe]

What type of loads are connected to this panel?

 

[waross]

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

 

[Selfentitled]

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!

 

[resqcapt19]

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.

 

[prc]

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..