Is the rating of a 400 amp bar type current transformer the panel max current?

[NEC_help]

Or is this a passive device. allowing the full feeder and OCD current to be used. (600A 3P fused fed by dual 350 mcm feeders)..

 

[petersonra]

If this is a CT used for metering it may be a problem, the POCO may have something to say about it.

If it is just for control and data collection, probably not an issue as long as the actual current stays below 400 Amps.

 

[NEC_help]

POCO would definatly be brought in..

POCO would definatly be brought in..

If this is a CT used for metering it may be a problem, the POCO may have something to say about it.

If it is just for control and data collection, probably not an issue as long as the actual current stays below 400 Amps.

The current needs of the building would exceed 400a.. so the POCO will be brought in to estimate if the CT's can be upgraded, and the pole transformers/service drop can handle the load. Old building, old panels, local businesses have all changed drastically from industrial factories to light power usage shops since this service was installed and rated by the utility. So we shall see.. thanks for your reply.

( unfortunately, I can not upload a pic..:happysad: )

 

[meternerd]

CT's are rated in ratio...i.e 400:5 and also TRF (Thermal Rating Factor). If the TRF is 2.0, the CT can handle 400 X 2 = 800A continuous without overheating. If it has TRF 4.0, it can handle 1600A.

 

[Tony S]

I was under the impression the thermal rating factor is also time factored as any transformer loading.

BTW, you don’t want to be around when one fails, I needed new underwear.

 

[epimetheus]

Thermal rating factors are continuous at a specified temperature, usually 30°C. Indoor CT's usually have a 55°C TRF as well. Check IEEE C57.13 for further details.

 

[meternerd]

CT's are rated in ratio...i.e 400:5 and also TRF (Thermal Rating Factor). If the TRF is 2.0, the CT can handle 400 X 2 = 800A continuous without overheating. If it has TRF 4.0, it can handle 1600A.

One thing I forgot to mention...maybe obvious....is to make sure the meter or secondary device is rated to handle 10A (RF 2.0) or 20A (RF 4.0). Most modern instrument rated Kwh meters are Class 20. Some after-market sub meters are not.