Basis for 120V cap to contollers

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Kodiak235

Kodiak235

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Kingsland, GA
I had a new piece of equipment come into the shops here recently that runs 230V single-phase through the controller. NFPA 79 9.1.2.1 limits the AC voltage to control circuits at 120Vac. What is the basis for this limitation? I'm likely going to reject this equipment because of this, but I couldn't find anything in the NFPA 70 to explain the basis for the 120Vac limit.
Where did this 120V limit come from, and is there any way to justify having a 230V control circuit?
 
ptonsparky said:
Interesting.

I am am not familiar with that reference...
Click to expand...

From the NFPA 79 - Electrical Standard for Industrial Machinery
---------------------
9.1.2 Control Circuit Voltages.
9.1.2.1 AC Control Circuit Voltages. The ac voltage for control
circuits shall not exceed 120 volts, ac single phase.


Exception No. 1: Other voltages shall be permitted, where necessary,
for the operation of electronic, precision, static, or similar devices used
in the control circuit.


Exception No. 2: Any electromechanical magnetic device having an
inrush current exceeding 20 amperes at 120 volts shall be permitted to
be energized above control voltage through contactor or relay contacts.
The contactor or relay contacts shall break both sides of the circuit
powering the magnetic device. The relay coil shall be connected to the
control circuit.


9.1.2.2 DC Control Circuit Voltages. DC control voltage shall
be 250 volts or less.

---------------

The controller this machine has uses a 230/230 transformer for the control circuit, so while it is separated from the motor currents it is still running 230Vac through the protective relays, on/off switch and emergency stop pushbuttons.

I'm just not sure where the exceptions are since I know there are a lot of machines in industry that utilize < 120Vac in their controllers. This controller is for the operation of a small <10A 3-phase motor so it doesn't meet the exceptions in the above articles.
Are there other exceptions in the NFPA 70 that I can use to accept this machine? This is quickly becoming another one of those head-scratching scenarios where I can't really think of a reason why this machine would be unacceptable except for the pretty plain black-and-white wording of this article.
 
Kodiak235 said:
From the NFPA 79 - Electrical Standard for Industrial Machinery
---------------------
9.1.2 Control Circuit Voltages.
9.1.2.1 AC Control Circuit Voltages. The ac voltage for control
circuits shall not exceed 120 volts, ac single phase.


Exception No. 1: Other voltages shall be permitted, where necessary,
for the operation of electronic, precision, static, or similar devices used
in the control circuit.


Exception No. 2: Any electromechanical magnetic device having an
inrush current exceeding 20 amperes at 120 volts shall be permitted to
be energized above control voltage through contactor or relay contacts.
The contactor or relay contacts shall break both sides of the circuit
powering the magnetic device. The relay coil shall be connected to the
control circuit.


9.1.2.2 DC Control Circuit Voltages. DC control voltage shall
be 250 volts or less.

---------------

The controller this machine has uses a 230/230 transformer for the control circuit, so while it is separated from the motor currents it is still running 230Vac through the protective relays, on/off switch and emergency stop pushbuttons.

I'm just not sure where the exceptions are since I know there are a lot of machines in industry that utilize < 120Vac in their controllers. This controller is for the operation of a small <10A 3-phase motor so it doesn't meet the exceptions in the above articles.
Are there other exceptions in the NFPA 70 that I can use to accept this machine? This is quickly becoming another one of those head-scratching scenarios where I can't really think of a reason why this machine would be unacceptable except for the pretty plain black-and-white wording of this article.
Click to expand...

I don't think NFPA 70 has any issues that would reject what you have described so far.

I don't know NFPA 79. Next question is whether it is an actual requirement to comply with it? NFPA 70 or an amended version of it is commonly adopted as law in many places, NFPA 79 maybe not a law but maybe a requirement by insurance or others or even just for a facilities own reasons.

I don't know if complexity of things factors into this or not, like I said I don't know NFPA 79. A lot of complex controls that run multiple motors and other equipment is commonly 120 volts or less and maybe even trending in more recent years to be under 50 volts for safety and the ability to work on it while energized reasons. Still pretty common to see simpler controls like for a single motor driven machine to have a control circuit that runs at same voltage as the motor circuit, but don't know if those actually comply with NFPA 79 or not.
 
kwired said:
I don't know NFPA 79. Next question is whether it is an actual requirement to comply with it? NFPA 70 or an amended version of it is commonly adopted as law in many places, NFPA 79 maybe not a law but maybe a requirement by insurance or others or even just for a facilities own reasons.
Click to expand...

We have a site directive here that requires equipment to comply with NFPA 79. Since someone raised the flag on this new machine (that's currently sitting on it's shipping pallet under a tarp) I've had a few other already in-use machines brought to my attention with similar control-voltage issues.
Has anyone here run into this or a similar issue, and how did you determine the safety of the factory-built equipment to place into use? It seems to me that running a 230V on/off switch shouldn't be that big of a concern - especially as it has a transformer and fuses to isolate it from the machine's running currents, but I'm hesitant to violate an established "common practice" and end up with lawyers involved.
 
What you are running into is that equipment in Europe and other IEC countries frequently use 230V control, in fact it is based on the line source being 400Y230, so the controls are L-N 230V. Then because they don't want to change their entire machine for us (where we do NOT have 400Y230V) they sometimes simply put in an isolation transformer to provide 230V L-L; the components don't care otherwise.

Nothing in the NEC (NFPA 70) or UL508 has any restrictions on control voltages, in fact 480V control is still available and perfectly legal (it's just that nobody likes to do that any more). NFPA 79 is a standard for "industrial machinery" and not everything is classified that way, hence it's not an enforceable standard in terms of AHJs etc. But if YOUR FACILITY has a requirement for that and that requirement was communicated to the machinery vendor, then I think you have a legitimate reason to reject the machinery.

But by the same token if that requirement was NOT communicated to the vendor, then that's the fault of your buyer. If that ends up being the case, you may be stuck having to change the control circuit yourself.

Just for future reference, the REASON machinery builders in other parts of the world don't like using 120V is because that only exists here (North America) for the most part, so when they go to buy coils for relays and contactors, they often have to wait for them. if you want to get around having this happen again, request 24VDC controls, which a LOT of foreign suppliers are switching to anyway. That way you end up with a Power Supply instead of a Control Transformer, and many (if not most) 24VDC power supplies now have a universal input, meaning they can accept anything from 80-285VAC input. So that way then send you the machine, you can connect 120V up to the power supply and everything works.
 
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