Service Load Calculations: Kitchens & Motors?

[Jon456]

I know that when calculating commercial service loads, we multiply the largest motor by 25% and add that to the load. But what if the largest motor is a piece of kitchen equipment?

Let's say I've got over 6 pieces of kitchen equipment. I've summed the load for each piece of equipment and I've applied the 65% demand factor from Table 220.56. Now I have the kitchen equipment load. But if one of those pieces of kitchen equipment is the largest motor in the facility, do I also add 25% of its load value to the motors section of the calculations? Or do the motor calculations only apply to non-kitchen motor loads (since the kitchen loads calculations already account for all kitchen equipment with and without motors)?

Additionally, would you consider a ventilation hood over a stovetop to be kitchen equipment? I would think it would be considered more like HVAC than kitchen equipment.

While I'm on the subject, could someone give me a quick summary of when you would use the "Optional Method" instead of the standard method of load calculations?

 

[PaulMmn]

An exhaust hood over a stovetop is kitchen equipment-- in a commercial setting, there is often a damper and a fire-alarm-triggered disconnect, so the exhaust fan doesn't encourage a fire. And a commercial exhaust fan can have a motor/squirrel cage fan combination to get a pretty darn good air flow going!

 

[Jon456]

I understand that it is physically part of the kitchen, and I'm well-aware of how it works and the safety features it incorporates. But my question is, in terms of NEC service load calculations, is it considered "kitchen equipment" like ovens, refrigerators, icemakers, mixers, etc. and thus subject to the same Table 220.56 demand factors.

 

[Dennis Alwon]

To use 220.56 the equipment must satisfy this part of the section-- I don't think a hood would do so.

These demand factors shall be applied to all
equipment that has either thermostatic control or intermittent
use as kitchen equipment.

 

[Dennis Alwon]

I also think if the largest motor was part of the kitchen equipment then it appears you would have to use the 125% but then still use the demand factor.

 

[Jon456]

To use 220.56 the equipment must satisfy this part of the section-- I don't think a hood would do so.

Thank you Dennis, I had read that before but had forgotten about it in this context. Trying to digest too much information at once. :huh:

I agree with you: it meets neither condition. In fact, for the majority of restaurants, a hood would be a continuous load.

 

[Jon456]

I also think if the largest motor was part of the kitchen equipment then it appears you would have to use the 125% but then still use the demand factor.

Ok. But typically the largest motor calculation is a separate step of the load calculations: the 25% is added as part of the motor loads where it would not be subject to any demand factor. So if the largest motor is part of the kitchen equipment, it seems we have two ways of performing the service load calculation:

1. Add the kitchen motor load as part of the kitchen equipment and apply the demand factor. Then add up all the other motor loads (not including the kitchen motor, because it's already accounted for in the kitchen equipment), but then add the extra 25% of the kitchen motor since it's the largest motor.

2. Add the kitchen motor load at 125% (because it's the largest motor) to the rest of the kitchen equipment and then apply the demand factor. Then add up all the other motor loads (not including the kitchen motor, because it's already accounted for in the kitchen equipment). No additional 25% is added to the motor loads because the largest motor was already accounted for in the kitchen equipment.

The difference is significant because in one case, the 25% addition is reduced by the kitchen demand factor, while in the other case it is not.

This would be a lot simpler if the largest motor were not part of the kitchen equipment!

 

[Jon456]

Here's another interesting problem I just thought about. What if your largest motor load was also a continuous load. Do you upsize the load by 125% then by 125% again? I think so, but I'd like to hear the opinions of others.

 

[Dennis Alwon]

Here's another interesting problem I just thought about. What if your largest motor load was also a continuous load. Do you upsize the load by 125% then by 125% again? I think so, but I'd like to hear the opinions of others.

No you only use 125% once, IMO