Minimum circuit ampacity

[Steelhead]

Hi Guys,

I'm looking for some help in the interpertation of 210.19(A)(1) when looking at the noncontinous load and the continous load.

For example I have a dedicated circuit supplying a piece of equipment where the nameplate says the max load is 75A. I know for this particular application that the continous load is 50A, but occassionaly the load jumps to 60A for a short time. In sizing the minimum circuit ampacity my thoughts would be 50A continous x 1.25=62.5A therefore I could size the conductors for a minimum of 75A (4 AWG = 85A @ 75degrees C)based on the nameplate, but not needing to size the conductors at 125% of 75A because the continous load is 50A not 75A.

OR

would you figure out the ampacity as 50A continous x 1.25=62.5A plus 60A (short duration load) which would equal 122.5A (1 AWG = 130A @ 75 degrees C)? This method seems like overkill to me. Which method would be correct based on 210.19(A)(1)?

Thanks

 

[david luchini]

Hi Guys,

I'm looking for some help in the interpertation of 210.19(A)(1) when looking at the noncontinous load and the continous load.

For example I have a dedicated circuit supplying a piece of equipment where the nameplate says the max load is 75A. I know for this particular application that the continous load is 50A, but occassionaly the load jumps to 60A for a short time. In sizing the minimum circuit ampacity my thoughts would be 50A continous x 1.25=62.5A therefore I could size the conductors for a minimum of 75A (4 AWG = 85A @ 75degrees C)based on the nameplate, but not needing to size the conductors at 125% of 75A because the continous load is 50A not 75A.

OR

would you figure out the ampacity as 50A continous x 1.25=62.5A plus 60A (short duration load) which would equal 122.5A (1 AWG = 130A @ 75 degrees C)? This method seems like overkill to me. Which method would be correct based on 210.19(A)(1)?

Thanks

I would say your load is 75A, non-continuous.

 

[GoldDigger]

:thumbsup:
And if you wanted to use belt and suspenders, you could calculate the continuous load at 50A plus a non-continuous load of an additional 10A, for a total of 72.5. Which is possibly how the manufacturer came up with the 75A figure they listed.
If the nameplate lists minimum circuit ampacity (MCA) instead of maximum load, there would be less room for confusion.

Tapatalk!

 

[cadpoint]

reposting...

 

[cadpoint]

210.19 is the Minimum Ampacity and Size. Branch circuits maximum loads in the 2011 is
220.18 Maximum Loads and read all of it plus (A)& (B).

...a piece of equipment where the nameplate says the max load is 75A.

While you gave a wealth of information, you didn't say what it was exactly, 220.18 might well be in play.

Also note Articles 430.7, 430.7(D), 430.24 > Which could be a real key for you.

I'm going to say it could be a various duty cycle motor(equipment), IE something else is kicking in to require more amps!

I'm going to show you how they came to the maximum for their name plate.

To do this focus on 430.21(E) Other than Continuous Duty, seethe Table 420.22(E)

Using Table 430.22(E)

Taken measurement peak of 60 amps;
60 x1.25 = 75 (standard continuous multiplier)
60 x1.2 = 72 (non size breaker but one rounds down in 440)

Taken measurement run of 50 amps;
50 x1.5 = 75 (30 -60 minutes rated motor) < I think this is it!
______________________________________________________________
Between 430 and 440 you do not have to consider any possible combinations of loads inside your equipment that are through out both articles, they did the work and put the maximum load on the name plate.

Mostly all Article 440 type equipment have "Name Plates" that state the exact maximum Ampacity that is needed. Other speciality equipment gives maximum lables and is require in
both subject articles. If it is 440 equipment, size to 75 Amps.

...a piece of equipment where the nameplate says the max load is 75A.

 

[Smart $]

The piece of equipment is evaluated as a whole unit. Given you know it does not draw 75A continuously for 3 or more hours, the entire piece of equipment is considered noncontinuous for the purpose of 210.19(A)(1). The minimum conductor ampacity is 75A as given on the nameplate.

 

[Steelhead]

Thanks guys!