Industrial Machinery - Article 670

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johnthompson

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Over the years my company has purchased many pieces of equipment used in various manufacturing processes. My question deals with the protection of these machines. According to articles 430.24, & 430.53 and other associated areas. You are to basically add up all the connected loads and protect accordingly. My contention is that these machines are actually considered ?Industrial Machines?, as such should be protected in accordance to article 670. Assuming this is true, should I consider the machines not built to the correct code section? Beyond that I don?t believe that I have the correct coordination because many of my mains are so grossly oversized compared to the actual running amps.
 
Re: Industrial Machinery - Article 670

Machines are not built to NEC standards. They are built to NFPA79 standards.

The requirements are a little different.

What problems do you think you have?

You still have to supply them power in accordance with NEC guidleines but the actually design and construction of the electrics inside the machiens falls outside of the NEC.

[ December 16, 2004, 05:54 PM: Message edited by: petersonra ]
 
Re: Industrial Machinery - Article 670

Look at the types of machines, elecric heaters, dc drives, control panels etc. You should have some one on site that would be able to give you load requirements for each piece of equipment, then address it accordingly.

Hank
 
Re: Industrial Machinery - Article 670

It?s true that industrial machine controls are installed according to NFPA 79, but the power to the machine and its protective devices are with the NEC. Historically, we have added up all the connected load (motors, heaters, etc) and supplied the protection and the utilities accordingly. We all no that industrial machines don't operate that way. Some of it will operate while the other sections waits for its turn. So the NEC article 670 allows for this. 670 basically says that you protect for the greatest load that COULD operate at any time. The question then becomes, if the machine is protected for total connected load, is it considered "Not to Code"? One thing is for certain, I have a coordination problem and a potential safety problem. For example, I have one machine that is protected with a 1200 amp breaker (the name plat shows 1177 amps of connected load), when measured, it never pulled over 400 amps. Now I have beakers, bus plugs wire and capacity that are too high for the application.
 
Re: Industrial Machinery - Article 670

Why do you feel you have a problem?

The feeder and branch circuit protective devices protect the conductors not the machinery. If your OCPD are sized correctly for the conductors you should not have a safety issue.
 
Re: Industrial Machinery - Article 670

Originally posted by jim dungar:
Why do you feel you have a problem?

The feeder and branch circuit protective devices protect the conductors not the machinery. If your OCPD are sized correctly for the conductors you should not have a safety issue.
Click to expand...
I agree. The individual loads inside the machine are protected by devices inside the machine control panel. The only thing you care about is protecting the wiring into the machine control system and making sure it is adequately sized to provide whatever power is needed.

Its not unusual to provide wired in backups for citical systems (like an extra hydraulic pump). But you would not see both of them operating at the same time. Its also rare to see anyone bother to figure out what the maximum load will really be. Its easier and "safer" to just total up the thing as if everything was on at the same time drawing full load.

And you never know just what might happen down the road. These things tend to change over time and stuff that may not have been run at the same time, might well run at the same time in a future revision of the machine.
 
Re: Industrial Machinery - Article 670

Of course the OCPD is sized correctly for the conductors. But let?s look at the coordination of the system. If there is a fault in the system, excluding the branch circuits, the main would not even see the fault. Potentially I could take out the connecting bus or substation. Then I?ll have more then just one line down, I could have half the building down. Ignoring all of that, let?s look at the cost of the equipment. A 600 bus plug would cost me approximately $5,000, where a 1200 amp would cost $13,000. Don?t stop there, the conductor size, the dedicated resources that can?t be used for other equipment and for new facilities with new processes (unknown loads) we have run into problems with local utilities. They think we are doing a bait and switch for special utility rates. We estimate 6 megs of load and then only pull 1 or 2. They have installed new substations, to support us?.it goes on an on. As far as safety, I?ll say one thing?NFPA 70E.
 
Re: Industrial Machinery - Article 670

I still don't see that oversizing the feeder creates a safety hazard. if the OCPD on the feeder is correct it protects the wiring up to the machine panel. The OCPDs inside the machine control panel protect from that point. There is no safety problem at all, anymore than there is a safety hazard in running a 400A feeder out to a panelboard and only using 20A from that panelboard.

There is nothing that prevents you from using some of that capacity for other things if you are confident it will never be needed for the machine, and in fact that is very common.

It seems to me this is strictly an economic issue.
 
Re: Industrial Machinery - Article 670

Think of it this way.

Say you have a 200 Amp 42 circuit panel filled with single pole 20A circuit breakers in it. Do you think you are ever going to draw 840 amps on the 200 amp main?

This is what the NFPA79 says:

17.4 Machine Nameplate Data.
17.4.1 Control equipment shall be legibly and durably marked in a way that it is plainly visible after the equipment is installed. A nameplate giving the following information shall
be attached to the enclosure:
(1) Name or trademark of supplier
(2) Serial number, where applicable
(3) Rated voltage, number of phases and frequency (if ac), and full-load current for each supply
(4) Ampere rating of the largest motor or load
(5) Maximum ampere rating of the short-circuit and groundfault protective device, where provided
(6) Short-circuit interrupting rating of the machine overcurrent protective device, where furnished as part of the equipment
(7) Electrical diagram number(s) or the number of the index to the electrical drawings
17.4.2 The full-load current shown on the nameplate shall not be less than the full-load currents for all motors and other equipment that can be in operation at the same time under
normal conditions of use. Where unusual loads or duty cycles require oversized conductors, the required capacity shall be included in the full-load current specified on the nameplate.
 
Re: Industrial Machinery - Article 670

Originally posted by kpepin:
Think of it this way.

Say you have a 200 Amp 42 circuit panel filled with single pole 20A circuit breakers in it. Do you think you are ever going to draw 840 amps on the 200 amp main?
Click to expand...
I agree with the theme if not the math. 21X20 = 420A each line.
 
Re: Industrial Machinery - Article 670

ok, it was late when I posted. Brain was on empty. But you get the idea.
 
Re: Industrial Machinery - Article 670

I have run in to this frequently for a manufacturing client - when is a 'thing' a multi-motor piece of equipment, an appliance, or an industrial machine?

The definition of industrial machine is pretty liberal, and I use it when I can and it makes sense. I do not use it "non-industrial" settings however.

As for your concern about the extra resources/materials used, etc. I see your point. But the solution might be to have the machine fabricator tighten up the nameplate data, to give you the real load data req'd. But if the fabricator is being lazy, or does not take the time to really figure it out, I think you are bound to use the nameplate data you're given.
 
Re: Industrial Machinery - Article 670

This turning out to be a much larger debate then I had anticipated. Thanks for all the comments.
Several of you have commented on my concern for safety. My company is on the tail end of implementing the NFPA 70E safety regulations, which has turned up a tremendous number of issues. The goal of 70E if you?re not aware is to provide the appropriate level of PPE for electrical workers when working on live equipment. To do this, you of course must know what your available fault currents are down to the equipment you?re working on. You must also know the clearing time and let through current of your protective device. Using the equations provided in 70E, you can then calculate the available energy in Cal/cm2. This will tell you the PPE level that you must protect to. Having said all that, the larger the protective device, the larger the potential let through current, the higher the PPE required, the more potential energy my electricians could be exposed to.

79 does tell you what and where the name plate goes, it also tells you how to protect it.
NFPA 79: states:
 1.4.1 "The size and over current protection of the supply conductors to a machine shall be covered by NFPA 70 (NEC), Article 670."

NFPA 79 further states in articles:
o 5.3.3.1(6)(a) Device must have 115% of the full load current of all equipment that can operate at the same time.
o 5.3.3.1(6)(b) Sum of all locked rotor currents of any load that can start and operate at the same time.

NEC Article 670 Industrial Machinery states:
 670.4 Supply Conductors and Over current Protection.
o 640.4(A) Conductor shall be sized no larger then 125% of the loads that COULD be in operation at the same time.
o 640.4(B) Over current device shall not be greater than 125% of the loads that COULD be in operation at the same time.
 
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