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Topic: Amperage Question

Dennis Benjamin
Phenomenal Film Handler

Posts: 1445
From: Denton, MD
Registered: Feb 2002

posted 08-13-2009 10:42 PM

OK - So, I am going on vacation tomorrow. The Turbochef oven died at our theatre and we really wanted to get it up and running by tomorrow. Since the parts did not come in for OUR oven, I drove down to Fredricksburg, Virginia to pick up another theatre's Turbochef.

So here is the dilemma: As soon as I picked up the oven, I noticed it was a different model. I went ahead and drove it back knowing that there may be an issue. Here is the problem: Our original oven is a 35 AMP plug with a different configuration than the 24 AMP plug that is on the borrowed Turbochef. Someone came up with the brilliant idea of switching out the plugs. I am uneasy with doing this since the amperage is different. Obviously they have different plug configurations so some dummy doesn't plug something into a socket that is rated correctly.

So, do we simply change out the plug? Or do I need to call in a professional?

Thanks.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 08-13-2009 11:18 PM

Really? 35 and 24A? Are you referring to the breakers or the plugs? The plugs will be higher ratings than the breakers.

I suspect your plugs are likely 40A and 30A if those are breaker ratings (or the faceplate ratings.

Normally, on the plugs (or receptacle) there will be the NEMA number. It will be something like 6-30 or L6-30 (the "L" is for locking). Common types are 5, 6, 14, 15. The first number determines the voltage and configuration. That is the 5 series is 125V with a neutral and ground. The 6 series is 250V (and 208), two hots and a ground. The 14 series are 4-wire...two hots, neutral and ground. These are for things that need 208-230 for things like heating elements but only 120V for control stuff. The 15 series are 3-phase 208V w/ground. There are others but these are, by far, the most common ones you will run into.

The second digit is the maximum amperage. So an 5-15 receptacle a 120V, 15A receptacle...aka a standard "Edison" household receptacle. If it were an L5-20, it would be a twist lock plug an rated up to 20amps.

Here is how the NEMA system/code works. The receptacle defines how much current the outlet may supply if it is the ONLY outlet on the circuit. A circuit breaker job is to merely protect the wire connected to it. So in a typical 20A theatre circuit, you are going to find a 12awg wire connected to it...unless it has to be derated due to length or fill in the pipe. Clearly, the breaker has no idea if you are hooking up a preshow projector or a walkie-talkie charger. All that breaker is responsible for is if the wire connected to it has exceeded its current...not the devices plugged into it.

Furthermore, you may also install outlets with smaller NEMA ratings (15A receptacles on a 20A breaker)...that is fine too. You are not endangering anything by not allowing higher current devices to plug in. In fact, in most homes, most outlets are 15A and are often on 20A breakers. The only requirement, code wise, is that the WIRE be large enough based on the breaker size. You are welcome to use larger wire size than the breaker too...you can wire your 20A circuits with 8awg wire...it will just cost more and be a pain to wire.

Now the other side of the coin is the device itself. It has to know its own power demands. That is, if it needs 16A, the manufacturer must install a 20A or larger plug on the device. This is YOUR protection. If you have 15A outlets and you have a 20A plug, they won't fit together. However, 20A outlets (straight blade only) will take 15A plugs just fine.

In fact, I dare say most of your stuff has vastly smaller current demands than the plug/outlet is rated for.

So lets look at this case...you are installing a smaller replacement unit than what you are taking out. For the sake of argument, lets say what you are taking out has a 40A plug and what you are putting in has a 30A plug. There is nothing legally or unsafe about putting a 40A plug on a 30A device. The 30A device will not exceed the current carrying capacity of the 40A circuit. Furthermore, the device, if it has UL or ETL ratings...which most jurisdictions require, it will have suitable current protection (breakers/fuses) right where the power comes into the unit to ensure that it does not exceed its current ratings.

You could NOT do the reverse though. You can not put a 30A plug on a 40A device as it will overload the circuit/wiring.

For help in identifying the NEMA standard plugs, you might try this web page:

http://www.twacomm.com/catalog/dept_id_963.htm

Steve

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