Motor Circuit Protector Allowed Uses.

[Skokian]

Mike & All --

In your opinion, are MCPs (Motor Short-Circuit Protectors) allowed to be
used outside of an Article 430 combination
motor controller? E.g.: Is it legal to use them to protect a motor branch
circuit?

Clause 430.52(C)(7) would seem to prohibit such use; but, Clause
250.122(D)(2) leaves me confused. See also
430.52(C)(3) (instant only C/B)

Your opinion?

Tx. in advance.

--
Regards . . .

Jim

P.S.: The question is due to reports of MCP's being used upstream of fire
pump controllers that I've heard of.

 

[weressl]

Mike & All --

In your opinion, are MCPs (Motor Short-Circuit Protectors) allowed to be
used outside of an Article 430 combination
motor controller? E.g.: Is it legal to use them to protect a motor branch
circuit?

Clause 430.52(C)(7) would seem to prohibit such use; but, Clause
250.122(D)(2) leaves me confused. See also
430.52(C)(3) (instant only C/B)

Your opinion?

Tx. in advance.

--
Regards . . .

Jim

P.S.: The question is due to reports of MCP's being used upstream of fire
pump controllers that I've heard of.

The UL listing would prohibit it's use outside of an approved assembly, but the application you are asking about is a pefect exaple where this device would fulfil the requirements of that particular Code section. It's one kind of a catch 22.

 

[templdl]

MCPs are component listed (reverse UR) and do not provide branch circuit protection because they have no overload (I2r) element, just an instantaneous/magnetic element.
If you provide branch circuit protection with a UL489 listed breaker first, up stream, then you can use a supplementary protective device down stream.
But remember that an MCP can not protect itself from an overload and will not service a load much more than its rating or you will let the smoke out.
Smaller MCPs actually have a solenoid type coil that the current travels through.
The lower the breaker rating the smaller the wire in the coil.
Therefore, too much current will smoke the coil and render the MCP useless.

 

[Skokian]

Motor Circuit Protector (MCPs) Allowed Uses.

Motor Circuit Protector (MCPs) Allowed Uses.

Great replies! Mucho thanks.

This is good ammunition for putting an end to the use of MCP's as Service Entrance Equipment, which is what's happening when they are used ahead of a fire pump controller.

Regards . . .

 

[ELR]

MCP's used for feeding input power to VFD's

MCP's used for feeding input power to VFD's

Perhaps the most common and egregious violation of NEC 430.52 (C)(3) that I see is where folks want to upgrade, say, an existing pump that was fed from a FVNR starter (with an integral MCP) to a VFD controller for the motor. Many times I have seen just that same MCP being used (no OL's) to protect the branch circuit feeding the VFD input. There is one vendor (a Japanese make) who even states that this is an acceptable practice! Does anyone else run into this? The standard practice should be to feed the VFD input power with an appropriately sized thermal-magnetic circuit breaker or fuses (which can single phase).