Multiple Momentary Heater Loads On Circuit

Status
Not open for further replies.

Mike-T

Member
Location
Liberal, KS
Have an application where 40 catalytic heaters would be installed in a building that only has 120v 1Ph service available. These heaters only require 120v power one time per year for about 1/2 hour to energize a heating element long enough to start the catalyst. Once started, the power is shut off and no longer required as long as fuel and air is supplied to the heater. The main problem is that each heater pulls 24amps for the 1/2 hour per year to get it started. Each heater can be started individually so the total load never exceeds 24amps, but the issue is the problem of having a connected load of 24amp x 40 heaters. Is there any exemption that would allow a PLC to interconnect all the loads on one circuit with relays to prevent more than one heater from ever starting at one time. Suggestions welcome. Note: This building is a class 1 div 2 area.
 

jumper

Senior Member
I am not sure but this may apply.

220.60 Noncoincident Loads. Where it is unlikely that
two or more noncoincident loads will be in use simultaneously,
it shall be permissible to use only the largest
load(s) that will be used at one time for calculating the total
load of a feeder or service.
 

renosteinke

Senior Member
Location
NE Arkansas
We have a similar code provision regarding heaters and air conditioning shering the same circuit. The key is preventing the different loads from operating at the same time.

You would certainly be allowed to do this with relays and timers; I see no reason that you could not use a PLC for the same purpose.

I do have some concerns, though. Your numbers suggest an entire day is needed to fire up everything- three days if we limit ourselves to 'business hours.' That certainly makes for "continuous" loading of the circuit. Allow for voltage drop, and we're looking at something more than a single extension cord :) There's no getting around that the design of the place needs some re-evaluation.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
I do have some concerns, though. Your numbers suggest an entire day is needed to fire up everything- three days if we limit ourselves to 'business hours.' That certainly makes for "continuous" loading of the circuit.

As soon as you turn off one heater, then turn on the next haven't you broken the continuous load "cycle". Meaning it is not a continuous load as far as the code definition is concerned.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
I am not sure but this may apply.

220.60 Noncoincident Loads. Where it is unlikely that
two or more noncoincident loads will be in use simultaneously,
it shall be permissible to use only the largest
load(s) that will be used at one time for calculating the total
load of a feeder or service.

This is a great reference. I guess since this applies to feeders The situation would be something like a 30A feeder the feeds maybe a fused disconnect at each heater?

As far as the PLC or relays I don't see any requirement for them. The operation of starting these would be well known to the operators and apart of the SOP would be starting one at a time.

Even though non-continuous by letter of the code, such a short time between starts would seem to make the effect that same. Anyway 30a feeder covers it.
 

kwired

Electron manager
Location
NE Nebraska
If you run too many at one time you will trip an overcurrent device. If that is not acceptable for the process then you need to design accordingly. Non simultaneous operating loads do not have to have an interlocking method to prevent simultaneous operation but is a good design sometimes.

You could also run multiwire or multiple circuits that will allow starting more than one at a time if that helps the process, you will need a starting scheme or some automation to the starting process to make things operate without overloading failures.

You could even run a separate circuit to each one so that any unit could be started simultaneously with other units but set a limit depending on available supply as to how many can be started at once. You could even monitor the current of the supply and have instructions that say once X amps is registered the system is fully loaded and no more units can be started.
 
Last edited:

Mike-T

Member
Location
Liberal, KS
Mike T, just exactly what type of facility is this ? Thank You

A gas compressor station far out in the middle of nowhere. Additional electrical service could be brought in, but due to the location and restrictions in the area, it would be cost prohibitive. The building was previously heated by a 4-million BTU steam boiler which has been taked out of service and will not be replaced. I appreciate all the input on this.
 

kwired

Electron manager
Location
NE Nebraska
A gas compressor station far out in the middle of nowhere. Additional electrical service could be brought in, but due to the location and restrictions in the area, it would be cost prohibitive. The building was previously heated by a 4-million BTU steam boiler which has been taked out of service and will not be replaced. I appreciate all the input on this.

All kinds of gas but none to use for heating??:)
 

John120/240

Senior Member
Location
Olathe, Kansas
If they were to use gas for their own purpose, they would have less to sell

to the end user.:lol: They probably have millions of cubic feet of gas in storage

but the pencil pusher & suits said no "Let's use electric heat"
 

renosteinke

Senior Member
Location
NE Arkansas
It sounds as if they ARE using gas for heat, but need the electricity to get the catalyst up to temperaure, get it hot enough to 'light,' so to speak.

I believe the code, as indicated by the specific reference to heat and A/C sharing a circuit, does require there to be some means of assurance that two of these loads will not operate at the same time. I do not agree that we can rely upon the breaker for this purpose. Now, I am 'deriving' this general rule from a specific - which might be a fault in my logic. In doing so, I am giving the OP the maximum lattitude. Others might deduce from the presence of a specific rule, it can be inferred that you are not allowed to do this- construing the code in as restrictive a manner as possible.

I believe that there must be some 'automatic' means to ensure that multiple loads do not operate at the same time. I do not agree that simple operator procedure is enough.

As for the 'counting' of the continuous cycle time: By the language, I agree that the changeover between units does mean that the load is not continuous. Yet, I see this as a continuous load in 'real' terms; those conductors will not have any opportunity to cool down in that moment between loads.

The OP commenting that this is a gas utility brings up another matter. I've worked a few such places, and each had back-up (gas fed) generators. I am surprised this one does not. A generator might allow for local generation of the power needed to ignite the heaters. Instead, it sounds like they're relying on the circuit for the yard lights to fill all needs.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
I believe the code, as indicated by the specific reference to heat and A/C sharing a circuit, does require there to be some means of assurance that two of these loads will not operate at the same time.

I believe that there must be some 'automatic' means to ensure that multiple loads do not operate at the same time. I do not agree that simple operator procedure is enough.

Do you have any code to back up these statements? The code reference previously listed by Jumper (220.60) about non-simultaneous loads uses pretty weak language saying the loads must be "unlikely" to operate together.
 

kwired

Electron manager
Location
NE Nebraska
Do you have any code to back up these statements? The code reference previously listed by Jumper (220.60) about non-simultaneous loads uses pretty weak language saying the loads must be "unlikely" to operate together.

Similar situation when using a generator with manual transfer switch. User is permitted to select the load to be used. If he selects too much it is going to open an overcurrent device.

In the OP situation if shutdown because of overloading can not be tolerated then I say it is a design issue and not so much a code issue.
 

renosteinke

Senior Member
Location
NE Arkansas
Twoskins ...

Any code references? Well, I was extending, as a general principle, 440.34, which makes mention of "where the circuitry is interlocked so as to prevent simultaneous operation ..."
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Twoskins ...

Any code references? Well, I was extending, as a general principle, 440.34, which makes mention of "where the circuitry is interlocked so as to prevent simultaneous operation ..."

Ok. I guess I understand your reasoning but I disagree that this is required for the OPs situation. While the general concept is mentioned in 440.34, it doesn't apply to the OP.

Interlocking may be prudent. But haven't seen code requiring it.
 
Status
Not open for further replies.
Top