ECN Forum Forums General Topics of the Trade General Discussion Area 2- 30amp receps

This subject touches on "design" issues...which is a good thing! Too many folks would consider any monkey with a pair of Kleins to be an "electrician," but only a true journeyman has the training, and experience, to make the sort of judgement calls required in design work.

As for the "Box" store: I have seen their clerks give decent advice; more common (in my experience) is the customer who doesn't want to accept what the clerk says, and just has to keep trying to make a mess of things.

Depending on the actual ratings of the equipment most likely yes.

However that was not the question, the question was about receptacles.

Quite frankly NEC rules that try to control the load that will be plugged into an outlet are ineffective at best.

The end users do not read the NEC, they often do not know how much power the equipment they plug in consumes.

There is no rule in the NEC that says I can not take a customers word as truth if they tell me they only want to operate one appliance at a time.


Consider 220.21. (I know it does not apply to branch circuits)


Notice it does not say the loads need to be interlocked only that they will not operate at the same time.

If the customer says I will not run these two widgets at the same time that is enough to satisfy 220.21

My point here is simply that this is strictly a design issue.

Of course two dedicated circuits will be more reliable.

Will two dedicated circuits make it safer?

I don't see how.

I am a firm believer in letting the person paying the bill decide what is best for them as long as it does not violate the code or result in an unsafe condition.

I will give them the benefit of my knowledge and make suggestions but ultimately it is their decision and if it happens they call me back in a month to add the things I recommended to start with I get the last laugh.

Bob

By the way, I don't buy into the '15 and 20 amp circuits are hard to overload' line of reasoning.

A hair dryer and a vacuum cleaner.

A coffee pot and a microwave. (Just because there are two kitchen circuits does not mean the load will always be dived between them.)

A portable heater and a large TV.

I tripped a 15 amp circuit at the house the other day for the first time in a while.

My wife was using a vacuum plugged into a circuit that a TV and 1,500 watt heater I was using was also on. After about 5 minutes it tripped no harm no foul, moved the vacuum to another outlet and I went back to watching TV.

Bob

Assuming that it's not a FPE breaker....

Bob,
"By the way, I don't buy into the '15 and 20 amp circuits are hard to overload' line of reasoning.'

I hope you dont think I was trying to imply that... What the customer does with a receptical is one thing if he says "I want an L6-30 right here, and a 6-30 there." But if he points to two 16A items.... "I want to use these on one 30A circuit." I'd say NO! That is not a design issue. 16X16=32, you now know that the intent is to exceed the OCP, and a violation of 210.20(A).



[This message has been edited by e57 (edited 03-26-2006).]

We can agree to disagree, I certainly respect your opinion and clearly you are driven by a desire to do the right thing.

From my point of view.

If the customer says;


I would ask if they mean at the same time or not.

If the customer tells me "No not at the same time" than there is no violation and I can proceed with the one circuit installation.

If the customer tells me "Yes at the same time" then I am obligated to refuse one circuit.

IMO what you are suggesting would be same as walking into someones home kitchen and adding up all the ratings of every plug in kitchen appliance they own and telling them that they must have enough circuits in the kitchen to power them all simultaneously.

Lets use another example.

You need to run a feeder to a garage that the customer is setting up as a well equipped wood working shop. This shop is strictly for hobby woodworking, one person working alone.

Planers, shapers, saws, drills lathes, lighting, HVAC etc.

Would you say the feeder must be large enough to supply all the loads at the same time?

After all it will all be connected and the customer could turn on everything at the same time.

Is the service to a typical house large enough to power all the electrical items the customer owns at the same time?

I guess it comes down to listening to and believing the customer.

If they tell "No not at the same time" and later they end up tripping the circuit because they did use them at the same time, I have not violated the NEC, they have.

Bob



[This message has been edited by iwire (edited 03-26-2006).]

Double pole - double throw switch?

I don't think these should be compared to a dwelling's kitchen appliances. This is utilization equipment. Personally, I read the NEC differently, and would not place these two items on one circuit sized for only one of them.
210.23 In no case shall the load exceed the branch circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it was rated. A branch circuit supplying 2 or more outlets or receptacles shall supply only the loads specified according to it's size as specified in 210.23(A) through (D).
210.23(B) A 30 amp branch circuit shall be permitted to supply... or utilization equipment in any occupancy. A rating of ANY ONE cord and plug connected utilization equipment shall not exceed 80% of the branch circuit ampere rating.
430.24 Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity of not less than 125% of the full load current rating of the highest rated motor plus the sum of the full load current ratings of all the other motors in the group..., PLUS the ampacity required for the other loads.
220.18 The total load shall not exceed the rating of the branch circuit and it shall not exceded the maximum loads specified in 220.18(A).
220.18(A) ... For circuits supplying loads consisting of motor operated utilization equipment that is fastened in place and has a motor larger than 1/8 HP in combination with other loads, the total calculated load shall be based on 125% of the largest motor load PLUS the sum of the other loads.
I can assume that the compressor has a motor, and will be fastened in place, and the welder is the "other load". Also, the NEC 2005 does not have 220.21 in it that I can see.

If we get back to reality for a second, lets look at my 20a circuits in the garage. One has a drop light, drill press, grinder, table saw and fan, plugged in all the time. There are also several open receptacles and a cabinet full of power tools. Certainly it is possible to turn them all on at once. More certainly it would trip the breaker.
Until I staff up this "shop" to run all of the tools, I won't need the extra circuits.
The same would be true with the pressure cleaner and the welder. Would you even want to turn on your welder if everything was wet?
I think that is safely a "noncoincidental load.

OK Bob and I will agree to disagree....

The items in say a garage or kitchen if connected would also be a violation, just as much as an 30A air compressor and 30A welder on the same circuit.

Like I said before, I think we can safely assume they are approching 20A ea (>15A continuous, or non continuous), or the would have been 20A ea, right?


It says load shall not exceed the continuous and noncontinuous loads, not intermitant, or single user loads. Right?


From Table 210.21(B)(2)

• 15A Circuit = 12A Max total cord-and-plug-connected load
• 20A Circuit = 16A Max total cord-and-plug-connected load
• 30A Circuit = 24A Max total cord-and-plug-connected load

Where does it say 'used at the same time'? It says "total cord-and-plug-connected load"

I think it is pretty clear....