Live parts inside enclosures

[petersonra]

Hi Bob,

out of the Siemens Handbook for UL "http://www.automation.siemens.com/tip-static/dlc/en/Low-Voltage-Distribution-Boards/The_Secrets_of_UL_and_NFPA.pdf"

Which standard applies?
Before configuration, it is necessary to clarify which standard is applied in which application cases. When to use UL 508A? When to use NFPA 79? When to use both?
The requirements and interfaces of both standards are clearly set out with regard to most points. If requirements overlap, however, the standard with the higher
requirements in relation to the respective point must be applied.

I was thinking, if something is not regulated in UL508A I have to look into NFPA79....

Not correct?

Andreas

You are misunderstanding how this stuff works.

In much of the US, the electrical codes do not require control panels meet either UL508a or NFPA79. They are both voluntary.

In some of the US, localities have added a requirement that control panels be listed. The only listing standard available for control panels is UL508a. One can also make a very good argument that OSHA requires control panels be listed although this requirement is widely ignored.

NFPA79 also covers other parts of the electrical design of machines that are not included in UL508a. However, it is a completely voluntary standard. Having said that, you have to design to some standard or you will incur liability in the court system. You can make up your own and defend it yourself, or you can use a widely recognized standard like NFPA79. It is just a lot easier and more cost effective to use NFPA79 over something else.

My understanding is that UL508a includes all the requirements for control panels that are also found in NFPA79. So, if one uses a UL508a listed control panel on an industrial machine, the control panel part already meets NFPA79. NFPA79 has additional requirements for things outside of the control panel, so using a UL508a control panel does not mean that the whole machine meets the requirements of NFPA79.

 

[petersonra]

I read this again.

Good morning and thanks for all the answers!

we don't get a label or a sticker from TUV Germany, we just get a report that our construction is able to get a occupancy permit.

There is no requirement for such a report in the US and it is doubtful that an AHJ would accept such a report for much of anything. As a practical matter, you are required to meet all the applicable requirements whether you present some kind of statement in writing that you meet those requirements or not.

This report we hand over to the local AHJ. He can use it or not...
I doubt they will do anything with it other than file it.


But our customers are the mayor tire brands. The local AHJ will be well trained to the machinary we deliver.
Most cases, an AHJ is not going to inspect a machine at all. they will look at the installation, but the design of the machine is generally not something they will look real close at.

If the NRTL give us a label before we deliver the machinery we can't make any changings during commissioning without loosing the label.
And we have make a lot of changings we don't know during design, add customer machines, additional tools.
This is not true. UL will not be coming back and taking away the label. The label just signifies that as it left the manufacturer, it met whatever UL listing requirements applied.

 

[GoldDigger]

I read this again.

If the NRTL give us a label before we deliver the machinery we can't make any changings during commissioning without loosing the label.
And we have make a lot of changings we don't know during design, add customer machines, additional tools.
This is not true. UL will not be coming back and taking away the label. The label just signifies that as it left the manufacturer, it met whatever UL listing requirements applied.

However, though the label may remain in place, it does not signify anything about the current state of the device.
The AHJ may not recognize that subtlety and contest the safety of the device though.

 

[petersonra]

​

However, though the label may remain in place, it does not signify anything about the current state of the device.
The AHJ may not recognize that subtlety and contest the safety of the device though.

The part in red is always true about every listed part ever made.

Listed parts and assemblies are routinely modified in the field and it is very rare that any inspector says anything at all about it. I do not mean it can't happen, just that it is rare.

 

[Jraef]

And just what is this insulation found on magnet wire if it is not lacquer?
It sounds like what is being said is that insulated magnet wire requires additional insulation and/or mechanical protection if it is used in a panel or for building wiring.

Insulation
Thermal Class-- Types
90 --------------- Paper
105 ------------- Paper, cotton
105 ------------- Solderable Polyurethane
105 ------------- Nylon
105 ------------- Polyvinyl Acetal, Formvar
130 ------------- Epoxy
130 ------------- Solderable Polyurethane
155 ------------- Polyester
155 ------------- Solderable Polyurethane
155 ------------- Glass
180 ------------- Polyester
180 ------------- Solderable Polyurethane
180 ------------- Solderable Polyester-imide
200 ------------- Polyester/amide-imide, AI
220 ------------- Amide-Imide
240 ------------- Polyimide

The lacquer is put on for physical protection against damage and to help prevent hygroscopic absorbtion of airborne moisture when de-energized. Dry type transformers always need something, epoxy encapsulated transformers take it to another level because they are going to be outdoors.

 

[Jraef]

The part in red is always true about every listed part ever made.

Listed parts and assemblies are routinely modified in the field and it is very rare that any inspector says anything at all about it. I do not mean it can't happen, just that it is rare.

It is very rare, but I have seen it once with an AHJ in Alaska in the 80s. I think that guy was an ex-UL inspector or something, he went over every panel with a fine toothed comb and pointed out UL violations right and left. Once I knew that about him, as a panel builder in Seattle I often used that to my advantage because when I saw a competitor "fudging" on even some minor issue on a project I knew was going to Alaska, I would put the fear of this inspector into the customer. His reputation was widespread up there, especially in the fishing industry.

One of his favorite issues was people who put things like VFDs and Soft Starters into MCCs as retrofit / panel shop additions. He knew the difference between a UL845 listing and a UL508A listing and would bounce any UL508A listing on a drive that was connected directly to the bus bars if it didn't come from the MCC mfr themselves, which in the 80s was basically any VFD. I was building control panels with VFDs for those customers that would be FED from breakers in the MCC, but every now and then I would lose a job to some poor lowballer who thought he would save money by putting the drives right in it. That put one guy out of business when a huge fish processing plant he built got red-tagged.

 

[Elektriker64]

Hello again,

sorry for the late reply, I was out to have a meeting with a customer in east asia.

Jraef: "But, again, if you are going for TUV certification, and TUV says they want to see it, you really have no choice."
On the long run, you are right.
But during the inspection, when the tester wants me to create a cover I ask him why. He told me "It is because NFPA79 / 4.2"
Me: Hm, really? This chapter tells me, I have to use components in their design ratings.
Tester: "Oh, no. I'm wrong, it is because NFPA79 / 6.2"
Me: "Yes, you are right. But the following Chapters told me to do how. 6.2.2 Protection by Enclosures and following. My chapter!"
Tester:"No. Inside an enclosure you still need protection against direct contact according to 6.2"
hmy:???

That was the moment I posted my question here.

The transformer is a listed device. The installation manual says nothing about additional covering, just to install it in a cabinet.
The vendors UL guy said, he didn't hear that before and I should not cover the transformer because of the heat flow.

Thanks

Andreas

 

[mgookin]

So according to this guy you could never have a buss in an enclosure?

 

[CEDEng]

A bit late to the party on this one - but, yep, er, nope, you cannot have exposed bus inside the cabinet, above a certain voltage.

I just finished having a UL/NFPA "Safety Guy" inspect three of my machines (I build them) - and he insisted we cover all the transformer terminals, or otherwise make them finger safe. Not just the transformers, but everything that could be touched with an errant finger AFTER the maintenance door is open and AFTER the Power Disconnect is defeated and AFTER the power is turned back on with the door open - there cannot be a live part exposed. None. (There is a lower voltage limit, maybe 48VAC, but i digress...)

Certainly it's a rare thing, but becoming less rare.

 

[Jraef]

Hello again,

sorry for the late reply, I was out to have a meeting with a customer in east asia.

Jraef: "But, again, if you are going for TUV certification, and TUV says they want to see it, you really have no choice."
On the long run, you are right.
But during the inspection, when the tester wants me to create a cover I ask him why. He told me "It is because NFPA79 / 4.2"
Me: Hm, really? This chapter tells me, I have to use components in their design ratings.
Tester: "Oh, no. I'm wrong, it is because NFPA79 / 6.2"
Me: "Yes, you are right. But the following Chapters told me to do how. 6.2.2 Protection by Enclosures and following. My chapter!"
Tester:"No. Inside an enclosure you still need protection against direct contact according to 6.2"
hmy:???

That was the moment I posted my question here.

The transformer is a listed device. The installation manual says nothing about additional covering, just to install it in a cabinet.
The vendors UL guy said, he didn't hear that before and I should not cover the transformer because of the heat flow.

Thanks

Andreas

He is over interpreting here.

"6.2 Protection from Electric Shock During Normal Operation.
Live parts operating at 50 volts rms ac or 60 volts dc or
more shall be guarded against accidental contact."

If the door is closed, it is guarded! NORMAL OPERATION, for a control panel, would be DOOR CLOSED. Door closed, no live parts.

I think you may have suffered from the same over interpretation CEDEng.