Heater MCA/MOCP

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sevis

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Baton Rouge, LA
Hi all,

The situation is that we have a hotel renovation which involves replacing fan coil units for all guest rooms. These units are hydronic cooling units with electric heat strips.

The question I have is 2 parts. For the units we are installing, the largest units have a 22A MCA and 25A MOCP. I have read many articles and seen videos by Mike Holt and others on the MCA/MOCP debate and we now abide by these numbers for HVAC equipment installations, so we are frequently installing wiring with smaller ampacities than the breakers. My first question is about article 240.4(D)(5) which states that #12 wire can't be protected by an overcurrent device larger than 20A unless there is an exception in 240.4(G).

240.4(G) contains an exception for Air Conditioning and refrigeration equipment circuits (440, Parts III and IV). I'm wondering why there isn't also an exception for heating equipment like I described above. Or am I thinking about this completely wrong? Is there another section of code that states that we can use the manufacturer provided MCA/MOCP on equipment regardless of the small conductor rules and exceptions?

The second question is that after diving into this hotel, we realized that several existing fan coil units are circuited together, sometimes up to 3 on a circuit. Considering that most of the existing units have an MOCP of 15, is it possible for them to be on 20A or 25A circuits without there being some kind of code violation or manufacturer warranty violation? As far as I can tell, there is no local overcurrent device like an enclosed circuit breaker adjacent to the units to help satisfy the manufacturer 15A MOCP requirement, so I'm wondering how these installations passed inspection.

Thank you for any help and I am happy to provide more information.
 
Heaters are static loads, they don't change when put ON. Heat pumps are motor-driven, they draw high currents during starting and the loading depends on whether the system is altered.
 
same answer as topgone on "why".. No inrush requiring a larger OCP device and no overcurrent device to protect the conductor such as you have with a compressor or motor load.

If the units call for a Max OCP of 25 amps that would need to be provided. Larger feeders could be installed but the individual unit would needs its listed protection.
 
I understand the response to the 2nd question - essentially you are stating that the HVAC equipment was installed in code violation, and in order for us to clean up the issue we will need to provide additional OCPD devices for each individual fan coil unit which meets the manufacturer MOCP requirements.

I guess I'm not understanding the response to the first question and maybe I didn't explain well enough. I don't believe these units are classified as heat pumps. The heat strips are electric resistance heaters, drawing a load of 2kw - 3kw (depending on the unit) during heating conditions. Essentially a cost analysis was done when the hotel was first built and it was decided that hydronic cooling, but electric heating was the best route to go, so they would only need 1 piping system through the building instead of 2.
 
Keep in mind a motor (compressor) HVAC units has in-rush current and factory overload in or in conjunction with the motor loads to provide overcurrent protection, so Art 440 exempts the requirements of 240.4(D).
You have no need for an oversized protective device (as there is basically no inrush) and you have no inherent protection so your heat strips are not listed in 240.4(G) and therefore not exempt.
 
If that's the case, then I guess I'm confused as to why air handling units and fan coil units with electric heat have manufacturer MCA and MOCP provided on the nameplates, if it can result in code violations in situations such as this (#12 with a 25A breaker)
 
sevis said:
If that's the case, then I guess I'm confused as to why air handling units and fan coil units with electric heat have manufacturer MCA and MOCP provided on the nameplates, if it can result in code violations in situations such as this (#12 with a 25A breaker)
Click to expand...

I understand your question and it is a good one. I think what you are looking for to validate this is Table 240.4(G) under "Motor operated appliance circuit conductors" (the same table that gives the permission you are familiar with on A/C and refrigeration). This refers you to Article 422 Part II. Part II will also refer to 422.62. Look a 422.62()B)(1).
As to your question about the multiple existing units with a MOPD of 15 that are connected to 1 20 amp OCPD, that is a violation.
 
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sevis said:
If that's the case, then I guess I'm confused as to why air handling units and fan coil units with electric heat have manufacturer MCA and MOCP provided on the nameplates, if it can result in code violations in situations such as this (#12 with a 25A breaker)
Click to expand...

Is that a violation?
 
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