Increasing Component SCCR Rating

[Dale Hayes]

Question:

Can a control transformer be used to increase the SCCR rating of an enclosure air conditioner unit by using a control transformer similar to what is shown on the attached page?

I need to maintain 65kA SCCR for a 380V, 3-phase, 800Amp Industrial Control Panel. The panel will include a side mounted 230V, 1-phase, 5A, 8000BTU enclosure air conditioner. The air conditioner has no SCCR rating. Every component in the panel other than the air conditioner is rated for 65kA.

Can I obtain the 65kA SCCR for the air conditioner by powering the air conditioner with a 380V to 230V Industrial Control Transformer that is fused on the primary side with two type CC ATQR fuses?

View attachment 5199

 

[mull982]

Question:

Can a control transformer be used to increase the SCCR rating of an enclosure air conditioner unit by using a control transformer similar to what is shown on the attached page?

I need to maintain 65kA SCCR for a 380V, 3-phase, 800Amp Industrial Control Panel. The panel will include a side mounted 230V, 1-phase, 5A, 8000BTU enclosure air conditioner. The air conditioner has no SCCR rating. Every component in the panel other than the air conditioner is rated for 65kA.

Can I obtain the 65kA SCCR for the air conditioner by powering the air conditioner with a 380V to 230V Industrial Control Transformer that is fused on the primary side with two type CC ATQR fuses?

View attachment 5199

If I understand your question correctly you are saying that your air conditioner does not have a listed SCCR rating. To my knowledge I did not think most loads came listed with an SCCR. I have never seen a motor or heater etc.. have a rated SCCR. These ratings as I have seen them have always been related to buswork, and protective devices.

Adding a control transformer would add an impedance and lessen the existing fault current capacity but without knowing what the existing fault capacity it you cannot say weather or not the transformer would keep the avaliable fault current below 65kA.

 

[SparkyHC]

Question:

Can a control transformer be used to increase the SCCR rating of an enclosure air conditioner unit by using a control transformer similar to what is shown on the attached page?

I need to maintain 65kA SCCR for a 380V, 3-phase, 800Amp Industrial Control Panel. The panel will include a side mounted 230V, 1-phase, 5A, 8000BTU enclosure air conditioner. The air conditioner has no SCCR rating. Every component in the panel other than the air conditioner is rated for 65kA.

Can I obtain the 65kA SCCR for the air conditioner by powering the air conditioner with a 380V to 230V Industrial Control Transformer that is fused on the primary side with two type CC ATQR fuses?

View attachment 5199

Can you re-state this question? The first sentence refers to "increasing" a SCCR rating, I expect that you meant "decrease"?

It appears as if your concerned about the available fault current that may be applied to the AC unit. First, are there fuses at where the main power enters this enclosure? Normally there is a disconnect which has fuses typically rated for interrupting capacity of 200,000 amperes.

If your concern is about the fuses let-through current then you will need the available short circuit from the feeder or supply and then with the documentation specific to the fuses installed the let-through at the AC can be ball-parked.

fpn....using a transformer to "limit" the short circuit current is a trick frequently used. A general equation for the short circuit current at the secondary of a transformer when the kVA rating and impedance "Z" is known is basically...
A = VA / (volts * sq rt of the phase) ( Z )

where sq rt 3 = square root of 1 when its single phase, 3 when three phase.
and where Z is the transformer impedance as a decimal....5% = .05

This equation assumes infinite short circuit available at the primary and ignores the contribution of connected motors and devices, but will get you somewhere near.

Seek the advice of a Qualified person if your not "sure" of your footing.

HC in NJ

 

[Jraef]

I think you may be over reaching a bit.

First off; 380V implies to me that it is not going to be installed in the USA, since that voltage is not available here. If so, SCCR means nothing, it is a requirement for the NEC, maybe the CEC (any Canadians want to confirm that?).

Second; SCCR ratings have only to do with POWER components, nothing below a "control power transformer" is part of the consideration. What you consider to be a "control power transformer" is pretty much up to you. Just make sure the CPT primary fuses are equal to or greater than the desired SCCR.

Third; Even if you were to power the AC unit from Phase-to-Neutral in your 380V system (assuming 4 wire), the AC unit is technically "outside" of the control panel, with a wire chase (hole) being used to deliver power to it. Essentially no different than a motor or any other "load" being fed from the control panel.

I wouldn't sweat it.

 

[jim dungar]

An SCCR is the rating of the device, without changing components you cannot change it.

You need to lower your available short circuit amps (SCA), through the addition of impedance (i.e. a transformer) so that it does not exceed an equipment's SCCR.

Do you know what your available fault current really is?