Equipment labeled with 37A MOCP is tripping 35 amp breaker

[SteamDonkey]

I think I already know the answer to this but I'd like to double check with you folks. Where an MOCP rating does not correspond with a standard overcurrent device rating is there anything in the NEC that allows the use of the next larger size device? When we contacted the equipment manufacturer about the 35A breaker tripping, they told us that NEC 240.4(B) allows us to use the next larger size (40A). My understanding is that 240.4(B) only applies to protection of conductors and has nothing to do with protection of equipment. Is that correct?

In my opinion the only way we could use a larger breaker is to have the mfr. re-label the equipment with a higher MOCP or provide something in writing from the mfr. that is acceptable to the AHJ.

Thanks.

 

[Fulthrotl]

I think I already know the answer to this but I'd like to double check with you folks. Where an MOCP rating does not correspond with a standard overcurrent device rating is there anything in the NEC that allows the use of the next larger size device? When we contacted the equipment manufacturer about the 35A breaker tripping, they told us that NEC 240.4(B) allows us to use the next larger size (40A). My understanding is that 240.4(B) only applies to protection of conductors and has nothing to do with protection of equipment. Is that correct?

In my opinion the only way we could use a larger breaker is to have the mfr. re-label the equipment with a higher MOCP or provide something in writing from the mfr. that is acceptable to the AHJ.

Thanks.

um, we are talking about THREE amps here......
put in a 40, and call it a day, or leave it there with a tripped breaker.

i don't see a third option.... :weeping:

 

[infinity]

IMO maximum means just that so in this case you cannot exceed a standard size OCPD of 35 amps. What type of equipment has an 37 amp MOCPD size sounds more like an MCA?

 

[jim dungar]

um, we are talking about THREE amps here......
put in a 40, and call it a day, or leave it there with a tripped breaker.

In the same regard, 2 extra amps is unlikely to trip a 35A breaker.

What is the load? I find it odd that it requires a non-stand protective device rating.

 

[Sierrasparky]

You can always get one of those new digital dial in breakers.

 

[SteamDonkey]

The equipment is some kind of refrigeration or HVAC unit for a grocery store. I'm not exactly sure because it's not my project, I'm just trying to help out a co-worker. Originally he was not provided with an MOCP figure, just an MCA which I think was 31 Amps. He ran #8 copper conductors from a 50A breaker and the inspector found the MOCP rating on the equipment and made us replace the 50A breaker with a 35A.

The manufacturer's solution was to up the breaker to a 40A "as permitted by NEC 240.4(B)." I don't think so.

For whatever reason we've found it's not that uncommon to get HVAC equipment with oddball MOCP ratings that don't correspond with a standard fuse or breaker size.

Thanks for the responses.

 

[GoldDigger]

32A MCA and 37A MOCP sounds a little close for comfort given the oddball numbers.
But the equipment should be capable of working with a 35A breaker.
Going to the limits of the MOCP is good practice to avoid occasional nuisance trips, but frequent trips at 35A makes me want to blame the equipment design. Or else the equipment is being used in some way beyond its rating.
Does it fail on motor start or after running awhile?
Has anybody measured operating current?

Tapatalk!

 

[texie]

The equipment is some kind of refrigeration or HVAC unit for a grocery store. I'm not exactly sure because it's not my project, I'm just trying to help out a co-worker. Originally he was not provided with an MOCP figure, just an MCA which I think was 31 Amps. He ran #8 copper conductors from a 50A breaker and the inspector found the MOCP rating on the equipment and made us replace the 50A breaker with a 35A.

The manufacturer's solution was to up the breaker to a 40A "as permitted by NEC 240.4(B)." I don't think so.

For whatever reason we've found it's not that uncommon to get HVAC equipment with oddball MOCP ratings that don't correspond with a standard fuse or breaker size.

Thanks for the responses.

See if this is of any help from UL: http://www.ul.com/global/documents/...trical/newsletters/EH&CMG_March2006_Final.pdf

 

[Gregg Harris]

IMO maximum means just that so in this case you cannot exceed a standard size OCPD of 35 amps. What type of equipment has an 37 amp MOCPD size sounds more like an MCA?

I would agree it is either MCA or a typo on the unit.

 

[kwired]

The equipment is some kind of refrigeration or HVAC unit for a grocery store. I'm not exactly sure because it's not my project, I'm just trying to help out a co-worker. Originally he was not provided with an MOCP figure, just an MCA which I think was 31 Amps. He ran #8 copper conductors from a 50A breaker and the inspector found the MOCP rating on the equipment and made us replace the 50A breaker with a 35A.

The manufacturer's solution was to up the breaker to a 40A "as permitted by NEC 240.4(B)." I don't think so.

For whatever reason we've found it's not that uncommon to get HVAC equipment with oddball MOCP ratings that don't correspond with a standard fuse or breaker size.

Thanks for the responses.

With a MCA of 31 I would expect to see MOCP of at least 50 for any across the line started units, something is being missed on interpreting that nameplate

 

[GoldDigger]

With a MCA of 31 I would expect to see MOCP of at least 50 for any across the line started units, something is being missed on interpreting that nameplate

Or in writing it!

 

[sparky=t]

it is quite possible there may be too much head pressure on the compressor, a lot of times this is over looked when troubleshooting refridgeration or cooling equipment. just a thought.

 

[kwired]

it is quite possible there may be too much head pressure on the compressor, a lot of times this is over looked when troubleshooting refridgeration or cooling equipment. just a thought.

Usually more of a problem with running motor overload protection though. The branch circuit device is generally high enough above full load current that it will not trip from high pressure unless the high pressure is preventing it from starting, generally more of a problem with single phase compressors than for three phase compressors as well.

 

[SteamDonkey]

I'm told the breaker was tripping a couple minutes after startup and the equipment was a rooftop condensing unit. It appears the issue was resolved in the field as we've not heard back from the contractor or owner for quite some time.

 

[M. D.]

Whacky numbers ... They may have called anotherE.C.

 

[kwired]

Whacky numbers ... They may have called anotherE.C.

Or had an HVAC contractor fix whatever was wrong with the unit:happyyes: