Engine Block Heater Calculations

[Jeff1971]

I have a project that requires installing 36 - 120 volt outlets to operate 1250 watt engine block heaters. 1250 watts divided by 120 volts = 374 amps. Does the NEC have a demand factor that can be used in the calculation (similar to RV parks, clothes dryers, electric stoves, etc.) to decrease the 374 amps to a lower value?

 

[LarryFine]

Is it possible to state with certainty the maximum number that will be in use at any given time?

Plus, remember that you'll be dividing this load by two or three, depending on 1ph or 3ph supply.

If it's 3ph, you'll be down to 125a per line.

 

[Cow]

Don't forget to figure them as a continuous load.

 

[boboelectric]

That job sounds like a gold mine.

 

[LarryFine]

If it's 3ph, you'll be down to 125a per line.

Ahem. Excuse me. :roll:

If it's 3ph, you'll be down to 125a.

 

[coulter]

... Does the NEC have a demand factor that can be used in the calculation (similar to RV parks, clothes dryers, electric stoves, etc.) to decrease the 374 amps to a lower value?

Living in an area where block heaters are a necessity: I hope not.

I would not consider this a code issue - it's a design issue. Consider this: Is the area one where block heaters are necessary? Does the customer wish to be able to fill the parking lot with vehicles and have them all plugged in and heated all the time? If the answers are, Yes, Yes, Yes - the application is 100%.

Here are some methods to reduce the power required.
1. Redude the number of spaces with receptacles. Consult with the owner, maybe some of the spaces can be unheated

2. Cycle the heater power using a timer, thermostat, and contactors feeding the panels. Consider:
above +20F off
+20 to -30F 50% duty cycle 30min on, 30min off
colder than -30F ON

Use two or four panels so you can drop the max current draw. If the area gets colder than -30F is won't help.

3. Put the transformers out in the parking lot, next to the panels. That will cut down on the fat runs.

carl

 

[ptonsparky]

I really like the idea of the timer and temperature cycling.

We use ground fault devices as well. The ground prong is always the first one broken off and yes the block heaters will be replaced more often.

 

[Jeff1971]

Engine block heaters

Engine block heaters

1. The engine block heaters a on a single phase service.
2. The outlets are at a FedEx distribution lot, therefore, it has the potential of all outlets in use at the same time (in Wisconsin).
3. Are these outlets required to be GFCI protected?

 

[RUWired]

3. Are these outlets required to be GFCI protected?

Yes...

(B) Other Than Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (5) shall have ground-fault circuit-interrupter protection for personnel:

(4) Outdoors

 

[frenchelectrican]

Jeff.,,

Yes the outdoor block heater recpectale must have GFCI on 15 or 20 amp 120v Circuit.


Coulter.,

That is a nice idea to use combation thermosast and timer.


Jeff ., Don't be suprised some of the block heater have much as 1500 watt so expect have some leeway in figures and you have to treat them with constant load figure due alot of the drivers leave the block heater on allnite { I done that all the time with my diesel truck but only used when it get colder than +5?F }.

Also a quick tip make sure you get the GFCI repectale with indicatior light{ LED } on it so that way the driver know they have power on the receptecle.

Merci,Marc