Portable generators and electric water heaters

By Dave Rongey Summary: Electrical Generator Question: Hi Dave I am in the planning stage of installing a portable home generator. I will be using a 65KW unit.

Portable Generators and Electric Water Heaters

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Generator Question:

Hi Dave I am in the planning stage of installing a portable home generator. I will be using a 65KW unit.

Most of the generator descriptions say that they are not suitable for use with hot water heaters and other things. Is this a blanket caution to prevent civilians from overloading their generators and causing warantee problems, or are generators not able to handle the momentary very high inrush current that occurs when a large heating element gets up to temperature?

I know nothing about how generators regulate themselves. I find the NEC a hard read. Does national or BOCA code prevent the use of separate branch circuits that are connected only to the generator?

I have seen such in Hospitals where there are red outlets in the wall that are generator connected only. I live in manufactured housing where this would be a much simpler way of doing the room and office wiring.
Thanks- Ray the civilian.

Hi Ray - Great Electrical Repair Question.
Due to the high consumption a electric water heater requires it is always recommended that water heaters are either not wired as one of the generator loads, or that the water heater be replaced with a gas fuel unit when prolonged outages are expected.

The same goes for any high wattage electrical appliance such as electric ranges and ovens as well. The load that is placed on the generator is substantial and lasts for a duration of time, depending on the size of the device. Problems can occur if a load such as this is present and then a motor is started such as a refrigerator, freezer, well pump or a septic pump which is typically 120 volts.

These motor loads have a higher inrush of current at the start which can place an unbalanced load on the generator, possibly causing an overloaded condition. An oversized generator can be installed to compensate for these loaded conditions while planning for a worst case scenario where the loads hit all at the same time, but this may prove to be costly.

I am not aware of any code that would prohibit any type of load being placed upon a generator. The generator size needs to be determined by the expected loaded conditions.

The generator manufacturer may prohibit some loads due to the design capabilities of the generator. That being said, portable generators are typically not designed for higher loads so you may be forced to consider a more substantial Stand-By generator for your power requirements.