Noncoincident loads article 220.60

[Tainted]

Suppose I have a dwelling unit and we are calculating the size for the main circuit breaker using article 220.

I have seen article 220.60 be applied to noncoincident Loads such as AC and heating but nothing outside of that..

If I connect relays to an electric stove and electric dryer such that these two items never turn on at the same time, will these two items be considered noncoincident loads and that means you can use the highest kVA value between the two?

 

[LarryFine]

I would agree.

 

[Tainted]

I would agree.

I can make the control circuit easy, what I'm worried about is what if the relay fails.

220.60 wording says "Where it is unlikely that two or more noncoincident loads will be in use simultaneously"

I would say a relay can "likely" fail and cause both to turn on at the same time

Edit: Or instead of relay, I can make a shunt trip circuit with 2 current sensing coils on both circuits

 

[winnie]

If you have a high enough amperage DPDT relay, it would take a very unlikely failure for both outputs to be energized at the same time.

Mechanical interlocks for contactors are also made for exactly this purpose.

E.g.

https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_magnetic_contactors/magnetic_contactor_accessories/bm0h

 

[Dennis Alwon]

Suppose I have a dwelling unit and we are calculating the size for the main circuit breaker using article 220.

I have seen article 220.60 be applied to noncoincident Loads such as AC and heating but nothing outside of that..

If I connect relays to an electric stove and electric dryer such that these two items never turn on at the same time, will these two items be considered noncoincident loads and that means you can use the highest kVA value between the two?

I would agree also however if your service is that close I would seriously think about an upgrade. lol

 

[don_resqcapt19]

I can make the control circuit easy, what I'm worried about is what if the relay fails.

220.60 wording says "Where it is unlikely that two or more noncoincident loads will be in use simultaneously"

I would say a relay can "likely" fail and cause both to turn on at the same time

Edit: Or instead of relay, I can make a shunt trip circuit with 2 current sensing coils on both circuits

Yet we permit a thermostat to do the same thing as that relay to prevent the simultaneous use of both heat and air conditioning, and the thermostat and its control system is just as likely to fail as the relay.

In the real world it does not make any difference if both loads are on at the same time. This is only a calculation rule used to size feeders and services. The worst case if both loads are on is that the OCPD will trip. There is no hazard.

I would have no issue with permitting a really so that you only use one load in the calculation.

 

[Tainted]

Yet we permit a thermostat to do the same thing as that relay to prevent the simultaneous use of both heat and air conditioning, and the thermostat and its control system is just as likely to fail as the relay.

In the real world it does not make any difference if both loads are on at the same time. This is only a calculation rule used to size feeders and services. The worst case if both loads are on is that the OCPD will trip. There is no hazard.

I would have no issue with permitting a really so that you only use one load in the calculation.

In my 5.5 years of experience starting out I have never seen noncoincidental loads be applied to anything other than AC units and heating. So I am trying to find any code reference that prevents from doing it..

 

[augie47]

As long as the conductors are properly protected if your system fails all that should occur is a tripped breaker.

If you want something more fail-safe install a double throw NF disconnect

 

[winnie]

I know that companies are making products specifically to create non-coincident loads, for example to permit an EV charger and a dryer to share the same circuit.

Dryer Buddy™ Plus AUTO

Don't have a 240v outlet in your garage? Get connected with a Dryer Buddy™ Plus AUTO! Allows your Dryer and EV charging station to use the same outlet without constant unplugging and re-plugging! Automatically switches the EV outlet on/off based upon whether Dryer is running or not. A handy...

www.bsaelectronics.com

I don't believe there are any code prohibitions to taking any optional circuits and combining them with some sort of interlock. I would argue that if code requires a circuit be instead (for example the 2 required SABCs or a bathroom circuit or the 120V laundry circuit) that you couldn't eliminate some of these required loads with an interlock.

But any optional loads? Interlocking them is a design choice.

Jonathan

 

[don_resqcapt19]

In my 5.5 years of experience starting out I have never seen noncoincidental loads be applied to anything other than AC units and heating. So I am trying to find any code reference that prevents from doing it..

The code does not care what the two loads may be...it only cares that they will not be running at the same time. It can be used for any two loads as long as they both are unlikely to draw power at the same time.

220.60 Noncoincident Loads.
If it is unlikely that two or more noncoincident loads will be in use simultaneously, using only the largest load(s) that will be used at one time for calculating the total load of a feeder or service shall be permitted. If a motor or air-conditioning load is part of the noncoincident load and is not the largest of the noncoincident loads, 125 percent of either the motor load or air-conditioning load, whichever is larger, shall be used in the calculation.