NEC 430 & Servo Motor Systems

[megloff11x]

I believe that NEC should provide a dedicated section for Servo Motor Systems under the Motors section. These systems are getting very sophisticated. They have added many very robust safety features to protect the motor and the machinery. They are used increasingly in factories for moving material and in machines, particularly robotics. The existing code doesn't "fit" well because the motor sizes and Voltages vary significantly from the standard sizes for induction & synchronous motors, VFD, and contactors. They are often mounted on moving parts, and thicker cable, even if properly ated for continuous flexing and twisting, will fail sooner than thinner cable. I've never seen one melt its wires. Inrush is also limited in more recent designs.

Is there a way to persuade the NFPA to get together with the foreign and domestic manufacturers of these systems and develop more specific standards?

It would be very nice from both the NEC and NFPA 79 to be able to use their firmware/software controlled limit and stop features in lieu of additional hardware. Several are working on getting their features listed for this purpose. I do believe that their built in functionality is faster and safer.

Matt

 

[petersonra]

what makes you think you cannot use the start/stop/limit functions built into these devices?

what additional hardware do you think you need?

the nec and nfpa79 are not product standards.

 

[megloff11x]

The various listing agencies tend to follow the NFPA standards closely, and have their own extra requirements on top of those. When you deviate, you invite extra scrutiny on the clock.

I have used them both in products and as standalone devices on the floor, where they would fall under NEC.

The built in stop functions on foreign made equipment are listed in their own countries, but identical and nearly identical wording is often not recognized here, and vice versa when you deal with CE.

 

[petersonra]

The various listing agencies tend to follow the NFPA standards closely, and have their own extra requirements on top of those. When you deviate, you invite extra scrutiny on the clock.

I have used them both in products and as standalone devices on the floor, where they would fall under NEC.

The built in stop functions on foreign made equipment are listed in their own countries, but identical and nearly identical wording is often not recognized here, and vice versa when you deal with CE.

I am curious just what you are talking about. You are being pretty vague. Perhaps you could elaborate.

CE is not a listing. It is a statement that the equipment taken as a whole meets ALL EU requirements. There is no testing required, and if you want to, you can self certify, and many companies do.

The fact that someone says something is "CE", means absolutely nothing in the US. In fact, if a system (as opposed to a component) is CE, it almost certainly does NOT meet US standards. Wire colors are different, the wire itself is different, the protection standards are different. That does not necessarily mean you are precluded from using such a machine or system in the US.

 

[megloff11x]

The standard practice is to make a US (black, white, green) and CE (blue, brown, green) wires version, but most other stuff stays the same. In the old days, transformers were tapped differently but today with switchers, that doesn't matter.

Every time I've been involved in these it has been drawn out with many last minute changes.

Going back to motors, I would love to be able to substitute the drive functions for some of the interlocking, and I would love to take advantage of the performance to use thinner wire. This is not to cut corners. The wire is moving with the parts and thicker wire fails more readily and requires greater effort to get strain relieved "just so."

Many of the drive makers don't use compatible terminology and their recommended installation doesn't always agree with NEC - so who do you follow now?

What I would like to see is more specific guidance that covers the finer points of these systems.

 

[petersonra]

Going back to motors, I would love to be able to substitute the drive functions for some of the interlocking,

What specifically are you objecting to? There is no reason you cannot use drive functions as part of your interlocking scheme. there is no specific prohibition against doing so.

and I would love to take advantage of the performance to use thinner wire. This is not to cut corners. The wire is moving with the parts and thicker wire fails more readily and requires greater effort to get strain relieved "just so."

The wire size is based on NFPA79, section 13.6 for motors used in machinery. Depending on the motor size you can go all the way down to 18 AWG.

Many of the drive makers don't use compatible terminology and their recommended installation doesn't always agree with NEC - so who do you follow now?

I believe you may be misunderstanding either the NEC or the manufacturer's instructions. You also may be misapplying the NEC where you should be using NFPA79.

What I would like to see is more specific guidance that covers the finer points of these systems.

The manufacturer's web sites are full of application guidelines and ideas. They also typically have people who are very good at helping you if you do not understand something.

We cannot help you unless you ask specific questions.