12/2 MC for 25a circuit

[mike93lx]

I'm working on a circuit for a steam humidifier. Aprilaire calls for a 25A, circuit, so I was going to run 10/2 NM-B, but I was wondering if 12/2 MC would work since the conductors are labeled thhn.

If I have this right, despite 12/2 MC using thhn, which has a 25a rating in the 75 degree column, I am limited to 20a per 240.4(D) unless the installation meets an exception in 240.4(G).

So, is a steam humidifier, which is installed at the air handler and can't function without the hvac system, "Air-conditioning and refrigeration equipment"? Or does that only provide for equipment with motors?

 

[mm08822]

The exceptions in 240.4G are for the circuits supplying motor driven Air-conditioning and refrigeration equipment...i.e. compressors, fans.

A steam humidifier is a mostly a resistive load and probably considered a continuous load. If so, then circuit conductors and ocp needs to be @ 125% of FLAs.

What do the installation instructions spec?

 

[mike93lx]

The exceptions in 240.4G are for the circuits supplying motor driven Air-conditioning and refrigeration equipment...i.e. compressors, fans.

A steam humidifier is a mostly a resistive load and probably considered a continuous load. If so, then circuit conductors and ocp needs to be @ 125% of FLAs.

What do the installation instructions spec?

Its a 16a draw, specifying a 25a circuit, hence that being what I'm designing for. Initially, I saw the 16a draw and was planning on 20a to accommodate the 125% sizing but they call for 25a for some reason, so that's what I'm doing.

Its not a long run, so it doesn't matter much anyway, just trying to learn and understand options.

The panel is close by and within sight, but I'm going to install a 30a dual pole switch at the unit for a disconnect. I'd rather not be using the breaker for service and shutting it down in the summers

 

[mm08822]

Based on the above info alone, it should be ok on a 12ga nm-b/ 20a cb. Possibly they are considering voltage drop and indirectly forced the 20A ckt to requiring #10's/25-30A.

Pic of nameplate?

 

[mm08822]

Could be it's the +10% possibility causing the bump up.

 

[mike93lx]

Based on the above info alone, it should be ok on a 12ga nm-b/ 20a cb. Possibly they are considering voltage drop and indirectly forced the 20A ckt to requiring #10's/25-30A.

Pic of nameplate?

Edit... You beat me to it.

I dont have it on hand, but the manual stage "16A +/- 10%", so that must be what is pushing it to a 25 circuit.

 

[mike93lx]

I had originally hoped to use 12/2 as I have a ton on hand, but I don't want to ignore the manual and I'd rather not limit output to save $75 in wire

 

[wyliesdiesels]

10/2 nm-b

 

[Bert_]

Post the nameplate anything else is guessing

 

[mike93lx]

Post the nameplate anything else is guessing

As has already been posted, I don't have it.

But that isn't really relevant. My question was if 12/2 MC could be breakered at 25a for the application. Feels like that is sorted

 

[PCustoms]

10/2 nm

Nm-b?

 

[mike93lx]

Nm-b?

Certainly. Nm is long gone

 

[dave*99]

How many gallons are needed? Seems it can cover a variety of outputs. I suppose I'd also wire it for the max, but the size of the house and how air tight it is determines gallons per day requirement.

 

[mike93lx]

How many gallons are needed? Seems it can cover a variety of outputs. I suppose I'd also wire it for the max, but the size of the house and how air tight it is determines gallons per day requirement.

I have no idea, that's part of why I want to go max. If it I was repuposing an existing circuit, I'd cut it back, but I have to run one anyway, and I happen to have a two pole 25 on hand, so the incremental cost is actually only $40 over 12/2 NM-B and the 11.5a setting.

Changing it to that lower output is just a dipswitch, so if I find the higher level excessive, I can drop it back to see if it saves money or manages humidity better

 

[PCustoms]

Certainly. Nm is long gone

I thought you could still use it, but only for 220?

 

[mike93lx]

I thought you could still use it, but only for 220?

Not sure if it can still be used, but I didn't think so. I would treat it as scrap.

 

[Steve W.]

I thought you could still use it, but only for 220?

220 is long gone, too.

.

 

[mike93lx]

220 is long gone, too.

.

220, 221, whatever it takes.

No need for the debate here. We all know what is meant

 

[micromind]

I'm working on a circuit for a steam humidifier. Aprilaire calls for a 25A, circuit, so I was going to run 10/2 NM-B, but I was wondering if 12/2 MC would work since the conductors are labeled thhn.

If I have this right, despite 12/2 MC using thhn, which has a 25a rating in the 75 degree column, I am limited to 20a per 240.4(D) unless the installation meets an exception in 240.4(G).

So, is a steam humidifier, which is installed at the air handler and can't function without the hvac system, "Air-conditioning and refrigeration equipment"? Or does that only provide for equipment with motors?

Article 440 of the NEC covers air conditioning and refrigeration equipment.

440.1 Defines the scope of the article and it states, basically, that it applies to motor driven equipment.

The exceptions to 240.4(G) (overcurrent protection) apply to part III and IV of 440 and those sections apply to motors.

Based on the above, it seems to me that the humidifier would be a separate piece of equipment that is controlled by the HVAC and not part of it as defined by 440.

The actual reality of it is that 12/2MC with a 25 amp breaker would handle 16 amps continuously for a very long time.

 

[PCustoms]

Not sure if it can still be used, but I didn't think so. I would treat it as scrap.

220 is long gone, too.

.

220, 221, whatever it takes.

No need for the debate here. We all know what is meant

That whooshing sound you just heard wasn't your HVAC...

For the record it's 240 and no NM is longer allowed. Was trying to have fun with correcting Wylie

 

[mike93lx]

Article 440 of the NEC covers air conditioning and refrigeration equipment.

440.1 Defines the scope of the article and it states, basically, that it applies to motor driven equipment.

The exceptions to 240.4(G) (overcurrent protection) apply to part III and IV of 440 and those sections apply to motors.

Based on the above, it seems to me that the humidifier would be a separate piece of equipment that is controlled by the HVAC and not part of it as defined by 440.

Thanks

 

[mike93lx]

That whooshing sound you just heard wasn't your HVAC...

For the record it's 240 and no NM is longer allowed. Was trying to have fun with correcting Wylie

I get it. Just trying to avoid 20 posts on 220v ********

 

[wyliesdiesels]

Nm-b?

not sure where one could buy nm but ok

 

[wyliesdiesels]

I thought you could still use it, but only for 220?

what? no NM can no longer be used and where did you come up with the 220 exception?

 

[mike93lx]

The actual reality of it is that 12/2MC with a 25 amp breaker would handle 16 amps continuously for a very long time.

I agree and that's why I was surprised at the 25a requirement. I assumed they set it at 16a specifically to allow a 20a circuit

 

[duneslider]

wrong place

 

[mike93lx]

wrong place

But what is the right place?

 

[duneslider]

But what is the right place?

That's getting a little too deep for me...

 

[mm08822]

not sure where one could buy nm but ok

I have about 100' of 12-3 NM for sale........any takers?

 

[mm08822]

The actual reality of it is that 12/2MC with a 25 amp breaker would handle 16 amps continuously for a very long time.

Even if we forget about the possible +10% mentioned by the mfr, #12 can't be breakered @ 25A in this application and still meet code.

 

[mike93lx]

Even if we forget about the possible +10% mentioned by the mfr, #12 can't be breakered @ 25A in this application and still meet code.

Although if the 10% wasn't needed, it likely could be breakered at 20a

 

[Norcal]

220, 221, whatever it takes.

No need for the debate here. We all know what is meant

If they don't know the fricken voltage they have no business doing electrical other then plugging items in & even that is suspect.

 

[mike93lx]

If they don't know the fricken voltage they have no business doing electrical other then plugging items in & even that is suspect.

Glad you stopped by. Thanks for the insight