80% rule

Status
Not open for further replies.
stickboy1375

stickboy1375

Senior Member
Location
Litchfield, CT
Do I have to derate any other branch circuits other than Cord and Plug Connected equipment not fastened in place? Or is it all breakers need to be derated to 80%? I can't seem to find what i'm looking for in the NEC....
 
The only 80% factor is for continuous loads and not many cord and plug connected loads qualify in reality, and as a matter of fact, not many residential loads would.

Roger
 
stickboy1375 said:
So 1800watts on a 15 amp circuit is okay? non continuous of course... I was always taught to derate...
Click to expand...

Yes it would if it were turned off every 179 min 59 sec's. :)

Roger
 
roger said:
Yes it would if it were turned off every 179 min 59 sec's. :)

Roger
Click to expand...

I agree and will add that the entire load does not have to switch off every 3 hours.
icon7.gif


The requirement is that the maximum load will not last longer than 3 hours.
 
Related question: would in-floor heat cable be considered continuous or non-continuous? Logically, the thermostat cycles the power, but what about the initial turn-on? What if the floor is only 40 degrees at first?

For that matter, you could say the same thing for any type of heat or air-conditioning: the first start-up of the season (or extended power failure or even a vacation) could see an over-three-hour initial running period.


Maybe the 80% only applies to 80% of the time, too? :D
 
LarryFine said:
Related question: would in-floor heat cable be considered continuous or non-continuous? Logically, the thermostat cycles the power, but what about the initial turn-on? What if the floor is only 40 degrees at first?

For that matter, you could say the same thing for any type of heat or air-conditioning: the first start-up of the season (or extended power failure or even a vacation) could see an over-three-hour initial running period.


Maybe the 80% only applies to 80% of the time, too? :D
Click to expand...


I don't see either the heat or the AC running for more than 3 hours if they are properly sized. Our old shore house would heat up in about an hour, even in the dead of winter when the heat had been off for weeks. Same thing for the AC in the summer.
 
Fixed electric space heating must be treated as a continuous load.

424.3(B)

Central HVAC will already have a circuit rated 125% of the load.

Electric water heaters less than 120 gallons also must be treated as a continuous load.

422.13
 
The 1996 NEC made changes to the rules for continuous loads that have generated more discussion and confusion than any topic that comes to my mind. We may be in for a replay.

Proposal 2-166 (pages 95-96) in the ROP has accepted the proposition that neutral conductors that connect to a neutral terminal (that is, not on an overcurrent device) and carry a continuous load shall be permitted to be sized at 100% of the continuous and noncontinuous load.
 
finhead said:
Proposal 2-166 (pages 95-96) in the ROP has accepted the proposition that neutral conductors that connect to a neutral terminal (that is, not on an overcurrent device) and carry a continuous load shall be permitted to be sized at 100% of the continuous and noncontinuous load.
Click to expand...
Great! Soon we'll have to stock cable with mixed conductor sizes. I can hear it now:

" . . . and a roll of 10-2/12-1."
 
210.21(B)(2) is max cord and plug connected to a receptacle, 80%, continuous load is not mentioned. 210.23(A)(1) and (2) 50% rule and 80% rule for cord and plug equipment, continuous load not mentioned. 210.23(B) 80%
 
Crankshaft, your references are dealing with single cord and plug connected loads on Multi-Outlet circuits, not total branch circuit capacity.

Neither 210.21 nor 210.23 would limit a single cord and plug connected load rated at 100% from being connected to a single receptacle circuit.

Even though "Cord and Plug Connected" was in the OP, the question was dealing with derating "Branch Circuits" and OCPD's.

Another problem with 210.21 and 210.23 is getting the end user to abide by the rules of the NEC.
icon12.gif


Roger
 
Status
Not open for further replies.
Top