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Hot Tub Overcurrent Protection


dtontarski
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I observed a hot tub install today and have a question about overcurrent protection. This was wired with four 8-gauge stranded copper conductors routed through rigid conduit and protected by a 50 amp GFCI circuit breaker.

The standard practice is that 8-gauge requires overcurrent protection by a 40 amp circuit breaker.

This stated, it is common for AC condensing units to have a minimum circuit ampacity requirement that allows for the use of smaller gauge conductors.

Do hot tubs have similar requirements. Do they have similar tags as AC units which specify the minimum circuit ampacity and min - max circuit breaker requirements?

There were no access panels on the skirting of this tub that supported the observation of manufacturer labeling.

Any advice would be appreciated.

Thanks.

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If the hot tub is considered multi-motor equipment and the manufacturer's nameplate has a maximum OL protection specification and minimum ampacity specification then those specs can be used.

The hot tubs that I've seen have only a single motor (pump motor).

Marc

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Marc,

Based on your response, and the fact that there is no observable manufacturer listing information, it sounds like I need to call this out for further evaluation.

This home has an updated service with several questionable conditions and no inspection label and I have already advised that they verify that this was permitted and inspected work.

Thanks,

Dave

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I observed a hot tub install today and have a question about overcurrent protection. This was wired with four 8-gauge stranded copper conductors routed through rigid conduit and protected by a 50 amp GFCI circuit breaker.

Just to clarify, you're talking about two hot conductors, a neutral, and a grounding conductor, right? Not some strange parallel configuration?

The standard practice is that 8-gauge requires overcurrent protection by a 40 amp circuit breaker.

This stated, it is common for AC condensing units to have a minimum circuit ampacity requirement that allows for the use of smaller gauge conductors.

That's because they're pure motor loads and the motors provide the overload protection.

Do hot tubs have similar requirements. Do they have similar tags as AC units which specify the minimum circuit ampacity and min - max circuit breaker requirements?

There were no access panels on the skirting of this tub that supported the observation of manufacturer labeling.

Any advice would be appreciated.

Since a hot tub includes, in addition to a motor, a heating element that uses a lion's share of the juice, no. I'd look for the data plate. If I couldn't find one, I'd size the conductors and the breaker as I would for any other heating circuit.

- Jim Katen, Oregon

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If they are individual conductors in conduit, they are more than likely #8 copper thwn conductors which are rated for 50A.

Most hot tubs I see require a 50A GFCI main and/or a split disco of 20/30.

I see no issue here and calling this out for further evaluation would more than likely make you look bad when the electrician gets there and does not find a problem.

What does your NEC say for the ampacity of a #8 copper conductor?

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Original quote by Jim:

That's because they're pure motor loads and the motors provide the overload protection.

Jim,

Would you clarify this for me, pls?

Marc

Sure. The air conditioner compressor has built-in overload protection that limits current on the circuit. The breaker or fuse in the panel is only there to protect against short circuits and ground faults; it's usually too large to provide overload protection. If it were sized to provide overload protection to the wires, then it would be at risk of tripping when the motor started up.

Michael Johnston does a much better job of explaining it in this article from IAEI Mag: http://www.iaei.org/magazine/?p=3944

- Jim Katen, Oregon

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I think what you are referring to is the thermal overload which is commonly installed within hermetic refrigerant units to protect the motor from overheat conditions. Although similiar to the thermal portion of a thermal/magnetic breaker, the application is not so simple as a breaker case. It's a refrigerant-cooled electric motor and refrigeration compressor installed within a sealed hermetic case and the engineering of this thermal device is likewise different. Overheat conditions may result from not only excessive current draw by the motor but from a host of other issues such as high head pressure, excessive suction temperatures or pressures, etc.

My understanding of the motivation of the code forming committee's 'multiple motors in a single appliance' rule is the desire to allow the manufacturer to engineer the ampacity/overcurrent protection of the circuit serving this appliance so that it will allow proper operation of the appliance without exposing the consumer to excessive risk of electrical fire.

Of course, this is just my opinion.

Marc

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I think what you are referring to is the thermal overload which is commonly installed within hermetic refrigerant units to protect the motor from overheat conditions. Although similiar to the thermal portion of a thermal/magnetic breaker, the application is not so simple as a breaker case. It's a refrigerant-cooled electric motor and refrigeration compressor installed within a sealed hermetic case and the engineering of this thermal device is likewise different. Overheat conditions may result from not only excessive current draw by the motor but from a host of other issues such as high head pressure, excessive suction temperatures or pressures, etc.

I agree with all that. The thermal overload functions as the overload protection device on an air conditioner circuit. It also provides the other protection you described.

My understanding of the motivation of the code forming committee's 'multiple motors in a single appliance' rule is the desire to allow the manufacturer to engineer the ampacity/overcurrent protection of the circuit serving this appliance so that it will allow proper operation of the appliance without exposing the consumer to excessive risk of electrical fire.

Of course, this is just my opinion.

You might be right about the motivation. I don't know. Which NEC section are you referring to (430.110©?) and how does this apply to the discussion at hand?

- Jim Katen, Oregon

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440.6 (B)

and it applies to this discussion via this mention of yours:

That's because they're pure motor loads and the motors provide the overload protection.

My point is that these thermal devices are engineered to protect the hermetic units from high temperatures which could damage them. They are not engineered for the purpose of protecting the electrical circuits that serve the appliance. That protection is separately engineered and is specified on the appliance nameplate in the form of minumum circuit ampacity and minimum/maximum breaker size.

Marc

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440.6 (B)

and it applies to this discussion via this mention of yours:

That's because they're pure motor loads and the motors provide the overload protection.

440.6(B) only says that you have to use the full-load current marked on the blower nameplate (instead of the horsepower rating) to determine the various characteristics of the circuit. I'm afraid I still don't see how this relates?

My point is that these thermal devices are engineered to protect the hermetic units from high temperatures which could damage them. They are not engineered for the purpose of protecting the electrical circuits that serve the appliance. That protection is separately engineered and is specified on the appliance nameplate in the form of minumum circuit ampacity and minimum/maximum breaker size.

I disagree. There are three parts to protecting the circuits: overloads, ground faults, and short circuits. The built-in overload protection in the compressor handles the first, and the breaker or fuses handle the others. If you were to rely on the breaker or fuses, you'd find that they're typically too large to do the job.

I cite three published sources for my opinion. The first is the article I referenced earlier at http://www.iaei.org/magazine/?p=3944. It says, "It may seem that the conductors are improperly protected. However it is the combination of the maximum size short-circuit and ground-fault protective device together with the overload protection system of the equipment that is providing the overcurrent protection for all circuit components."

The second source is Douglas Hansen's "Electrical Inspection of Existing Dwellings," which says, "Large motors and air conditioners separate these overcurrent functions. The breaker or fuse ahead of the air cinditioner only protects against short circuits and ground faults. Overload protection is built into the compressor itself."

The third is Mike Holt's, "Motor & Air Conditioning Calculations, Unit 7," which says, "The Code definition of “Overcurrentâ€

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