Feeder circuit for electric heaters

[augie47]

As is usual, I read until I confused myself and I'm unsure who takes what stand, not that it matters.
Charlieb sums up my thoughts precisely in Post #36

 

[jim dungar]

... then the wire to the unit would be calculated at 104 amps but the feeder could be 83 amps. This makes no sense and I doubt there would be an inspector around that would pass that install.

The heater feeder cannot be smaller than its largest branch circuit, 220.51.

 

[Dennis Alwon]

The heater feeder cannot be smaller than its largest branch circuit, 220.51.

Thanks Jim-- I even mentioned that earlier and forgot, but my point is the same. In the case of one heater the load is 104 for the feeder and the other- with the same exact load but separate branch circuits the load is 84 on the feeder.

 

[iwire]

Thanks Jim-- I even mentioned that earlier and forgot, but my point is the same. In the case of one heater the load is 104 for the feeder and the other- with the same exact load but separate branch circuits the load is 84 on the feeder.

No, the load is the same on both feeders.

 

[jumper]

As is usual, I read until I confused myself and I'm unsure who takes what stand, not that it matters.
Charlieb sums up my thoughts precisely in Post #36

I like this part the best.

I have lost track of who is supporting which point of view, and I strongly dislike the statements I have read that convey such messages as, ?you lack comprehension.? It is OK to say, ?I disagree? or ?I believe you are wrong.? It is NOT OK to say, ?you don?t understand what you are talking about.? Let us stay civilized, or find someplace else to debate.

Oh yeah, the technical stuff was good also.:grin:

 

[Dennis Alwon]

No, the load is the same on both feeders.

The load is the same however the calculated load is different in the 2 cases. Thus we need a larger wire in one scenario then the other.

 

[iwire]

The load is the same however the calculated load is different in the 2 cases.

No, and I have to give Charlie credit for bring it to my attention.

At no time does the NEC say we add 25% to the load.

The code does require we size the conductor to 125% of the load.

There is a difference.

Thus we need a larger wire in one scenario then the other.

Not once all of 220.51 is applied.

 

[Dennis Alwon]

No, and I have to give Charlie credit for bring it to my attention.

At no time does the NEC say we add 25% to the load.

The code does require we size the conductor to 125% of the load.

There is a difference.

Are you saying in the 2 cases I presented the size of the feeder would be the same? I think not. If the branch circuit is sized at 125% then in the case of a single unit with 20K heat the wire must be sized to 104 amps. In the example of he op we are saying the feeder only needs to be sized for 84 amps. Do you agree?

 

[iwire]

Are you saying in the 2 cases I presented the size of the feeder would be the same? I think not. If the branch circuit is sized at 125% then in the case of a single unit with 20K heat the wire must be sized to 104 amps. In the example of he op we are saying the feeder only needs to be sized for 84 amps. Do you agree?

I will split it with you.

The load, the calculated load, remains the same.

The wire size required for the same load changes as does the use of the conductors.

IMO, as I pointed out before, it is much more likely for one heating unit to remain on for 3 or more hours than it is for a 2 or more units to all run together for the same 3 hours.

OR, it is just another harmless code oddity.:grin:

 

[ActionDave]

I will split it with you.

The load, the calculated load, remains the same.

The wire size required for the same load changes as does the use of the conductors.

IMO, as I pointed out before, it is much more likely for one heating unit to remain on for 3 or more hours than it is for a 2 or more units to all run together for the same 3 hours.

OR, it is just another harmless code oddity.:grin:

That is the answer right there. It is not a code oddity but one of the times the code makes good sense. A branch circuit to one heater could see max current for three hours, maybe. The feeder for multiple heating units is never going to see the maximum current from all the heaters for anywhere near three hours, ever.

Never. NEVER EVER. Never never, ever ever.



Well may once, but then never again and so there would be no real insulation damage.:roll:

 

[Dennis Alwon]

The feeder for multiple heating units is never going to see the maximum current from all the heaters for anywhere near three hours, ever.

Never. NEVER EVER. Never never, ever ever.
:roll:

The only reason I brought this up was because the OP said the units will run at the same time. If that is the case there goes your never, never, ever, ever theory.

 

[iwire]

The only reason I brought this up was because the OP said the units will run at the same time. If that is the case there goes your never, never, ever, ever theory.

So these units have no thermostats? All four of them are expected to run more then 3 hours continuously at the same time? Seems odd.

Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more.

I think people get far to wrapped up worrying about continuous loads.

 

[Dennis Alwon]

So these units have no thermostats? All four of them are expected to run more then 3 hours continuously at the same time? Seems odd.

I think people get far to wrapped up worrying about continuous loads.

I have no idea- it was what the op said so I played with it. Assuming they have separate t-stat then that changes things but that is not what the op said. At least that is how I took it- one T-stat with 4 units.

Each of these heaters will be located in a storage conex, and each heater will be running at the same time.

 

[ActionDave]

The only reason I brought this up was because the OP said the units will run at the same time. If that is the case there goes your never, never, ever, ever theory.

You left out the part where I said it could happen.
But even without t-stats the elements change resistance as they heat.
For continuous load we need max current for three hours.

 

[One-eyed Jack]

I have lost track of who is supporting which point of view, and I strongly dislike the statements I have read that convey such messages as, ?you lack comprehension.? It is OK to say, ?I disagree? or ?I believe you are wrong.? It is NOT OK to say, ?you don?t understand what you are talking about.? Let us stay civilized, or find someplace else to debate.

That said, I will, without looking back to any earlier statements or citing anyone else?s previous comments, simply give my views. Take them or leave them, as you choose.

1. To start with, I infer that we are discussing a single feeder that serves a panel that, in turn, has four branch circuits, each serving a single heater, and that no other loads are to be served by that feeder.
2. I submit that the calculated load on each branch circuit is 20.8 amps (which I will join the others in rounding to 21), and not 26 amps. Basis: Part II of 220 does not require us to add 25% to continuous loads.
3. I submit that the minimum ampacity of the conductors in each branch circuit is 26 amps. Basis: 210.19(A)(1) tells us to size branch circuit conductors for 125% of continuous load, and 424.3(B) tells us that, for the purposes of sizing branch circuits, a space heater is a continuous load.
4. I submit that the calculated load on the feeder is 84 amps, and not 89 amps (i.e., 125% of the first heater and 100% of the other three), nor is it 105 amps (i.e., 125% of the total for four heaters). Basis: 220.40 tells us the feeder load is not less than the sum of the branch circuit loads, after demand factors are applied, and the rest of 220 does not give us any demand factors for heaters.
5. I submit that the minimum ampacity of the conductors in the feeder is 84 amps, not 105 amps. Basis: 215.2(A)(1) tells us to size feeder conductors for 125% of continuous load, and nothing, not even 424.3(B), tells us that, for the purposes of sizing feeders, a space heater is a continuous load.

Despite all thoughts and expectations we may have concerning lunacy versus consistency, a heater is considered a continuous branch circuit load, and a non-continuous feeder load.

I agree with you Charlie,100%.