Load calcs for receptacles - general use or not

[electrofelon]

Say we are doing feeder or service calcs for a commercial laboratory. 220.44 sends us back to 220.14 which uses the phrase "general use receptacles." What exactly does this mean? There seems to be a lot of ambiguity here. My interpretation is that the 180 VA per yoke is for a receptacle that we do not know what is going to be plugged into it. Strangely , if you think about it, the 180 VA in 220.14(I) is not restricted to NEMA 5-15/5-20 outlets as one might assume. I have a hard time considering most receptacles other than 5-15/20's as "general use". Im just trying to get a better feel for this since I am putting plans together for this lab and much of the equipment is cord and plug connected with a 5-15. There is Lots of refrigeration type equipment. Problem is they cant commit to locations of anything, and I know it will change so getting this thru plan review is a hassle. To what extent can I just call most things "general use receptacles" and count them at 180VA?

 

[LarryFine]

You're correct about the general definition: non-specific loads, hallways, offices, waiting rooms, etc.

For your specific purposes, maybe do an equipment count and a receptacle count, and use the ratio to come up with a reasonable receptacle-per-circuit number, or if you know each load, calculate a receptacle-per-circuit that way.

Also, are you considering MWBCs? That can also have an effect on your circuit count and distribution.

 

[oldsparky52]

Also, are you considering MWBCs? That can also have an effect on your circuit count and distribution.

I'm confused, how does using a MWBC effect the circuit count?

 

[electrofelon]

You're correct about the general definition: non-specific loads, hallways, offices, waiting rooms, etc.

For your specific purposes, maybe do an equipment count and a receptacle count, and use the ratio to come up with a reasonable receptacle-per-circuit number, or if you know each load, calculate a receptacle-per-circuit that way.

Also, are you considering MWBCs? That can also have an effect on your circuit count and distribution.

Yeah there will be a bazilion circuits for the NEMA 5's and I will use MWBC's. Ive worked for this company for years in their other labs and you just cant count on anything. I have to go in all the time to add circuits because they moved/added equipment around and breakers are now tripping, or they used extension cords to got yelled at by the fire marshal. I just feel a bit dishonest calling a lot of these "general use", but without better information and with all their changes, there isnt much I can do.

 

[electrofelon]

I'm confused, how does using a MWBC effect the circuit count?

A MWBC is technically one circuit, although that seems like just a technicality and cant think of when that would come into play.

 

[kwired]

A MWBC is technically one circuit, although that seems like just a technicality and cant think of when that would come into play.

It would still be 180 VA per receptacle for general use receptacles you just have two or three times the capacity for the entire circuit as you have on a two wire line to neutral circuit.

 

[electrofelon]

So its seems like the honor system with these receps. Say I have a commercial fridge or freezer that has a 5-15 plug and draws 8 amps. I can denote a recep for that as dedicated equipment with a load of 960VA, or I can claim ignorance and count that recep as "general use" at 180VA?

 

[LarryFine]

I'm confused, how does using a MWBC effect the circuit count?

My bad. I meant the quantity of circuits run to each receptacle point.

 

[Knightryder12]

I usually calc these known loads for receptacles based on the information given during design and put them in as a misc. load. That way those items do not have any diversity associated with them. Sometimes, well all of the time, this makes my panels larger. But to me that's OK because of like you said, you cannot trust those lab guys to not move equipment around or bring in addiational.

 

[gadfly56]

If you have MWBC's and for some reason lose the neutral, aren't you in danger of letting out the magic smoke if the loads aren't balanced? Maybe not an issue for the DVD player, but you'd hate to lose a Mettler precision balance at $2K a pop.

 

[electrofelon]

If you have MWBC's and for some reason lose the neutral, aren't you in danger of letting out the magic smoke if the loads aren't balanced? Maybe not an issue for the DVD player, but you'd hate to lose a Mettler precision balance at $2K a pop.

Anything is possible, but I dont really consider that likely enough to be a consideration. I have considered NOT running MWBC's for them in case they want to convert a circuit from 120V to a 208V, and 3 single poles are significantly cheaper than a 3 pole, however with the number of circuits I feel I need to cover all their changes, it gets into a zillion CCC's and pipes.

 

[Cow]

So its seems like the honor system with these receps. Say I have a commercial fridge or freezer that has a 5-15 plug and draws 8 amps. I can denote a recep for that as dedicated equipment with a load of 960VA, or I can claim ignorance and count that recep as "general use" at 180VA?

This is exactly correct. Do the best you can with what you know. I'm not sure why a person would calc a recep at 180va when you know you may have a 960va dedicated load plugged in???

We do plan reviews all the time for things that aren't even close to nailed down, just broad strokes. We just make our best effort to cover ourselves and the customer, we haven't had any plan reviews or services come back to bite us later, yet.

 

[electrofelon]

This is exactly correct. Do the best you can with what you know. I'm not sure why a person would calc a recep at 180va when you know you may have a 960va dedicated load plugged in???

Well it depends if are we talking service/feeder or branch circuit. For service/feeder, even with some "cheating" on some of this unknown equipment,
I know the NEC calcs are so conservative, Ill have plenty of capacity. Furthermore, I have a very good sense of what these places draw having worked in many of their other facilities so I know what do design for regardless of NEC. For branch, its just a balancing act of providing enough circuits to cover "most" situations without going crazy resulting in $20k more work. They like quads everywhere, and I am leaning toward somewhere around 3 quads/6 duplex per circuit.

 

[kwired]

You also need to know some details of the load and how it is used. You could have multiple items that have heavier draw but either seldom run at same time or maybe have pretty short run time when used on same circuit and never have any troubles holding the breaker.