HMCP and Bi-Metallic Overload for XFMR protection

[MrJLH]

While performing some NETA testing on a breaker inside one of our substations I came across a HMCP and bi-metallic overload being used to protect a three phase 75kVA transformer. Although not ideal is there any reason this installation would not be acceptable per NFPA70?

Thoughts?

 

[ron]

I believe the Eaton Cutler Hammer model HMCP is itself a Thermal Magnetic Circuit Breaker, so it is a UL Listed product for the application. A bi-metallic overload, typically listed on its own (used for motor protection) is typically not listed as an assembly with an HMCP breaker unless it is in a motor starter.
From a functionality standpoint, it may be fine, but it doesn't seem that it would be a listed installation and may not comply with 110.3(C)

 

[don_resqcapt19]

I believe the Eaton Cutler Hammer model HMCP is itself a Thermal Magnetic Circuit Breaker, so it is a UL Listed product for the application. A bi-metallic overload, typically listed on its own (used for motor protection) is typically not listed as an assembly with an HMCP breaker unless it is in a motor starter.
From a functionality standpoint, it may be fine, but it doesn't seem that it would be a listed installation and may not comply with 110.3(C)

Pretty sure that is a motor circuit protector with magnetic (instantaneous) trip only.

Product Description
Designated as Eaton’s Types GMCP and HMCP, the instantaneous-only motor circuit protector (MCP) is available in ratings from 3 A to 1200 A for motor starter sizes 0 through 8.

If that is the case, the product was listed as a motor starter and not suitable for protecting a transformer.

 

[David Castor]

AFAIK, the HMCP (and the MCP) are instantaneous-only breaker with no thermal element. They can only be used in a combination motor starter in conjunction with a motor overload relay. In my opinion, using this for transformer protection, even with the addition of the overload relay would be a violation of the UL listing for the HMCP.

 

[Jraef]

No, it’s not going to meet Code.

HMCPs are NOT UL listed, they are UL Recognized components that can only be used as part of a factory assembled and listed motor starter assembly. There is no other approved use. So anything else will be a violation of 110.3(B).

Besides, an OL relay only acts to drop out the coil circuit if a contactor in the motor starter. Without the contactor, it does nothing.