MCA and MOP From Article 440

[fifty60]

Article 440.4(B) requires me to list the MCA and MOP on the equipment nameplate. Do I have to list the EXACT MCA, or am I able to use a larger number. For example, if my MCA calculates out to 26.9A, is it acceptable to just state an MCA of 30A on the nameplate?

Same thing with the MOP, but in the opposite direction. If the MOP actually calculates out to 50A, but I know a 40A OCPD works well, am I able to use 40A as the nameplate MOP or do I have to use the MOP as calculated?

 

[petersonra]

Article 440.4(B) requires me to list the MCA and MOP on the equipment nameplate. Do I have to list the EXACT MCA, or am I able to use a larger number. For example, if my MCA calculates out to 26.9A, is it acceptable to just state an MCA of 30A on the nameplate?

Same thing with the MOP, but in the opposite direction. If the MOP actually calculates out to 50A, but I know a 40A OCPD works well, am I able to use 40A as the nameplate MOP or do I have to use the MOP as calculated?

440.4(B) points you to part IV. That sections uses the term "not less than" when referring to ampacity. That suggests to me you can put any number you want as the MCA as long as it equals or exceeds the calculated number.

 

[fifty60]

That is definitely helpful. Regarding the MOP, does it have to be the absolute MOP, or can it be anything less than or equal to the MOP? The MOP seems to be more straight forward than the Minimum Overcurrent Protection. Using 430.62 and 430.63, I cannot determine what the "minimum" OCPD needs to be. Am I able to use 125% of the largest motor, and then 100% of the continuous loads, etc, or do I have to use the lowest percentage from Table 430.52 which is 175%.

 

[petersonra]

That is definitely helpful. Regarding the MOP, does it have to be the absolute MOP, or can it be anything less than or equal to the MOP? The MOP seems to be more straight forward than the Minimum Overcurrent Protection. Using 430.62 and 430.63, I cannot determine what the "minimum" OCPD needs to be. Am I able to use 125% of the largest motor, and then 100% of the continuous loads, etc, or do I have to use the lowest percentage from Table 430.52 which is 175%.

there is no minimum. it is a design choice. I usually like to make it as large as I can to reduce the chance of a nuisance trip.

ETA: I would point out there may be an advantage to not rounding up the MCA. It is possible that it might force the end user into going to a larger size wire than he would need if it was noted as being slightly less. It is unlikely in most cases, but some weird combination of wire insulation, number of CCC, and ambient temperatures might make the required ampacity slip to the next larger sized wire.

 

[fifty60]

Thanks again. I know some people that think the OCPD that is specified for the equipment in some way correlates to the service size the user of the equipment has to use. I believe this is misguided. The machines I deal with range from 20A FLA to 100A FLA. I think the FLA is all that matters to the end user, and the MCA. If I am stating some "minimum" OCPD does not give any advantage to the end user to stating a "Maximum".
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They also think that the OCPD specified somehow affects the "Service" size for the end user. Any thoughts on this would be helpful as well. THey think that the true MOP would make the equipment less attractive than stating the Minimum OCPD.

 

[petersonra]

IMO, give the end user the most choice by stating the bare minimum MCA and absolute maximum overcurrent protection.

If they want to use bigger wires or lesser rated CB that is a design choice as well.

 

[Jraef]

I think you may have misinterpreted something. MCA is the MIMIMUM Circuit Ampacity, MOCP (not MOC) is MAXIMUM Over Curtent Protection. If you correct that perception to reality, your question is answered in the definitions.

You can state the MCA as being any value OVER what you calculate, but just realize that it affects / limits the choices of the end user.

You can at the same time specify an MOCP to be ridiculously lower than you know will work, with the caveat that you may increase your customers' frustration level, the trouble calls you receive and ultimately limit your customer base to people who have never bought your product before or talked to anyone who did. That ultimately relieves you of the problem too, but not in the way you want...

 

[fifty60]

I just need help explaining to marketing and sales level folks that specifying a true MOCP should not affect anything...that the only numbers that truly matter are the MCA and the FLA.

If I am running a machine that is drawing 24AMPs as an FLA, what difference to the customers energy requirements would it make if we make the MOCP 30A or 40A? I definitely understand what Jraef is saying, and I would like to have better intuition regarding how this would affect the customers power requirements...

 

[fifty60]

The UL handler for the equipment said that as far as he is concerned, according to the standard the machine is listed under, that all that needs to be on the nameplate is Voltage and FLA. The standard does not have any requirements for MCA or MOCP.

Is it then acceptable to only list the FLA and Voltage on the nameplate? The equipment has refrigeration compressors inside of it, so it falls under article 440 which requires the MCA and MOCP. Since it is listed, does it need the rest of the information on the data tag or is the fact it is adhering to the listed requirement satisfactory?