How to Figure FLA's of machine ?

Guy's I have a somewhat off topic question for ya.
We build machines that have as many as 20 motors on them, All the motors are started through a sequence routine in the PLC. Starting 2 seconds apart.
For a Givin Machine how should I figure the Full Load Amps Required by the machine? This has always been done by basically adding up all of the motors, controls etc. And always multiplying the largest motor by 1.25
However knowing that there is no way the FLA will ever reach anything near that number, Due to the starting routine. Should I calculate this differently ?? THANKS For any input !

I want to take you seriously on this but I don't see how any of us can answer this question with any precision.

I say that because, what you are really asking is "how close do I dare to come to the point where nuisance fuse clearing occurs".

Or, you could just as well ask us or yourself to predict just how much overload your machine will see with, say, 100 different operators.

Your question is an excellent example of how engineering is not all about numbers. You have to add JUDGEMENT and that can't be taught in school very well. Even long experience leads us astray sometimes.

Sorry, but we all have to manage risk, even in technical fields.

Just my quick $.02. It won't take someone long to reprogram the starting sequence to turn everything on at once. I've always been on the conservative end and done all my FLA by looking at my hardware and disregarding how it will be programmed, because I've been bit before where someone smashed all my motor contactors on at once, then complained that everything was engineered incorrectly.

The FLA is just 100% of each motor and non-motor load. Conductor sizing and fuse sizing is where the 125%, 150%, and 300% come into play, though that generally is an electrician's job to size.

Main conductor sizing:
125% of FLA of largest motor plus
125% of continuous non-motor load plus
100% of FLA of all other motors plus
100% of FLA of non-continuous non-motor load

Maximum fuse sizing (dual-element time-delay type only):
150% of FLA of largest motor plus
125% of continuous non-motor load plus
100% of FLA of all other motors plus
100% of FLA of non-continuous non-motor load

Maximum fuse sizing (non time-delay and all class CC only):
300% of FLA of largest motor plus
125% of continuous non-motor load plus
100% of FLA of all other motors plus
100% of FLA of non-continuous non-motor load

If you are looking to fuse one motor the optimal fuse size is usually 200% of FLA for class CC and 150% for class J fuses.

Thanks Everyone for the Info,

Very Helpfull.

Matt,
The way you described it in your own post is the basic NEC Article 430 requirement. Programming has nothing to do with it. If your facility is required to follow the NEC then the feeders and main OCP needs to be sized as you described. There may be an obscure NEC exception (ie: under engineering supervision, etc.)but this is the basic rule.

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RE: Kittydog42's comment of "that generally is an electrician's job to size"
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Most electricians and electrical contractors will disagree with that statement. They feel (correctly) that it is the engineer's job to provide that design and show it on the drawings. The problem is that too many programmers that have no electrical experience are responsible for designing things and many do not even know how to size wire or even that the NEC exists.

dogleg43 said:

Most electricians and electrical contractors will disagree with that statement. They feel (correctly) that it is the engineer's job to provide that design and show it on the drawings. The problem is that too many programmers that have no electrical experience are responsible for designing things and many do not even know how to size wire or even that the NEC exists.

Click to expand...

That is more accurate. We both agree that the programmer should not get his pickle ticklers into it.

milmat1 said:

This has always been done by basically adding up all of the motors, controls etc. And always multiplying the largest motor by 1.25

Click to expand...

What you are referring to is the supply conductor requirement of NEC article 430.24. I think what you are looking for would be covered by 430.62. Basically the same idea, without the 1.25 factor. Are the motors/controls individually protected in the machine or do you just have one main honkin breaker?

edit: Actually, this (430.62) is the calculation for the main breaker/fuse. Maybe not what you are looking for now that I think about it.

Matt, I'd like to apologize for my earlier posting on this. I completely missed the code issues you were asking about.

I should have just left it for the electricals on the board here. For some reason, I thought you were referring to the internal wire design technique inside your product where you were already way over code requirements.

Milmat,

If you put a label on the machine that says FLA or Full-Load Amps, then it has come to have some legal (NEC Code) meanings.

Starting current has a slightly different meaning than Full-Load Amps. You can reduce the initial total motor starting current by staggering the motor starting times, but this does not necessarily reduce the "FLA" of the machine. By reducing the starting current it may be possible to use a smaller main fuse or breaker. Again, this is not directly dependent on the machine rated FLA.

jedft said:

What you are referring to is the supply conductor requirement of NEC article 430.24. I think what you are looking for would be covered by 430.62. Basically the same idea, without the 1.25 factor. Are the motors/controls individually protected in the machine or do you just have one main honkin breaker?

edit: Actually, this (430.62) is the calculation for the main breaker/fuse. Maybe not what you are looking for now that I think about it.

Click to expand...

All are Individually protected. And One main Breaker for the Machine in front of everything.
My question was certainly answered, THANKS.

We build an engineered product that is not covered under NEC However the practices remain similar. Due to the fact that once the machine is installed in the Factory, Any modification, or Additions etc. are covered under NEC as I understand it .....


Again THANKS !!

We build an engineered product that is not covered under NEC...

Click to expand...

Unless your engineered product falls into one of the following categories, then it is covered by the NEC.

National Electrical Code Article 90.2(B) Not Covered. This Code does not cover the following:
(1) Installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles.
(2) Installations underground in mines...
(3) Installations of railways...used exclusively for operation of rolling stock.
(4) Installations of communications equipment under the exclusive control of communications utilities...
(5) Installations under the exclusive control of an electric utility...

Specifically, unless your product is battery-powered, I think it would certainly be included in NEC Article 90.2 Scope (A) Covered (3) Installations of conductors and equipment that connect to the supply of electricity.

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RE: LANCE1 COMMENT OF: Unless your engineered product falls into one of
the following categories, then it is covered by the NEC.....
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Lance, I'm not trying to argue with you but are you sure your statement is correct? There seems to be a lot of different opinions about this.

The NEC defintion of Premises Wiring says "........Such wiring does not include wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment."

Have all local or state authorities adopted the NEC? And then what version have they adopted?

For the protection of their own reputation and their customers' interests, many architect and consultants' specifications require control systems and machinery installations to follow the NEC.

After an accident OSHA puts the squeeze on people by referring to standards that are not actually adopted by OSHA (example: NFPA 70E).

Yes, that is the NEC definition of "not Premises wiring". But there is nothing in the NEC, except the list in 90.2(B), that excludes these other items (that are not part of the premises wiring) from meeting the intent of the NEC.

I don't think anybody would want to say that the NEC doesn't cover the size of the wires, or the size of the overcurrent devices, even though the "engineered product" is not part of the premises wiring.

The National Electrical Code has been adopted with the force of law by most states, cities, and counties in the US, plus several other countries. So many have adopted it in the US, that the remainder don't count for much. They are the anomolies, the rebels, or the don't-cares.