Electrical Engineering - Can panelboards be equipped with control circuits?

Author

Can panelboards be equipped with control circuits?

Danny

2007-09-26, 9:25 am

In an NFPA protective clothing class I'm attending, there was a
question about what type FR clothing should be worn when working on a
125VAC energized control circuit. From the job hazard analysis
matrices we were handed out, the only mention of "control circuits"
were for MCCs(motorized control centers). The descriptions of typical
jobs in 240VAC or less panelboards didn't mention any control
circuits....just energized parts.

Yes, the question is vague and poorly worded...yes, in the real world,
I would know whether I was working on a panelboard or a MCC or some
sort of other cabinet. I guess my question boils down to whether
NEC's definition of a panelboard can include the use of a control
circuit enclosed within? I googled panelboard and "control circuit"
together and didn't seem to find any relevant hits.

Any examples or model numbers if such a beast exists would be
appreciated. Also, if someone knows the NEC and OSHA's 1910 backwards
and forwards and knows that control circuits aren't in panelboards,
I'd appreciate a reference.

Thanks in advance.

Danny

gfretwell@aol.com

2007-09-26, 1:25 pm

On Wed, 26 Sep 2007 06:19:07 -0700, Danny <hokiewolf@hotmail.com>
wrote:

>In an NFPA protective clothing class I'm attending, there was a
>question about what type FR clothing should be worn when working on a
>125VAC energized control circuit. From the job hazard analysis
>matrices we were handed out, the only mention of "control circuits"
>were for MCCs(motorized control centers). The descriptions of typical
>jobs in 240VAC or less panelboards didn't mention any control
>circuits....just energized parts.
>
>Yes, the question is vague and poorly worded...yes, in the real world,
>I would know whether I was working on a panelboard or a MCC or some
>sort of other cabinet. I guess my question boils down to whether
>NEC's definition of a panelboard can include the use of a control
>circuit enclosed within? I googled panelboard and "control circuit"
>together and didn't seem to find any relevant hits.
>
>Any examples or model numbers if such a beast exists would be
>appreciated. Also, if someone knows the NEC and OSHA's 1910 backwards
>and forwards and knows that control circuits aren't in panelboards,
>I'd appreciate a reference.
>
>Thanks in advance.
>
>Danny

Generally speaking the panelboard is the assembly inside the cabinet
that holds the overcurrent devices. If the cabinet was large enough it
could also contain other equipment. I have seen assemblies that
include the service disconnect, branch circuit O/C protection and MCC
equipment in one cabinet. The sewer lift pump controllers you
sometimes see on the side of the road is one example. It comes as a
listed assembly.
For the purposes of arc flash protection this is really a distinction
without a difference. You should be protected for the available arc
hazard, no matter what kind of equipment you are working on.

Gerald Newton

2007-09-26, 8:25 pm

On Sep 26, 5:19 am, Danny <hokiew...@hotmail.com> wrote:
> In an NFPA protective clothing class I'm attending, there was a
> question about what type FR clothing should be worn when working on a
> 125VAC energized control circuit. From the job hazard analysis
> matrices we were handed out, the only mention of "control circuits"
> were for MCCs(motorized control centers). The descriptions of typical
> jobs in 240VAC or less panelboards didn't mention any control
> circuits....just energized parts.
>
> Yes, the question is vague and poorly worded...yes, in the real world,
> I would know whether I was working on a panelboard or a MCC or some
> sort of other cabinet. I guess my question boils down to whether
> NEC's definition of a panelboard can include the use of a control
> circuit enclosed within? I googled panelboard and "control circuit"
> together and didn't seem to find any relevant hits.
>
> Any examples or model numbers if such a beast exists would be
> appreciated. Also, if someone knows the NEC and OSHA's 1910 backwards
> and forwards and knows that control circuits aren't in panelboards,
> I'd appreciate a reference.
>
> Thanks in advance.
>
> Danny

Control circuits do exist in panelboards in the form of controlled
SCR's on the mains, CT's on the branch circuits, etc. These
panelboards should be listed by a nationally recognized testing lab
like UL and the contol contractor installing the controls should have
a UL certification.
The phrase "control circuits" doesn't mean much. You have to go by
the Class. Class 2 control circuits are not a shock and fire hazards
in a nonclassified (nonhazardous) environment. However Class 1
control circuits are.
For further info read Article 725 in the NEC.

I talked to an OSHA man in Washington DC several years ago about
NFPA70E. He said that OSHA asked the NFPA to write the document, but
that they were having difficulty getting it adopted.
Some major players are complaining that calculating the available
fault current is not an exact science, and there are four computer
programs that do the calculation but they do not give the same
answers.

At the IAEI NW Section meeting I went to about two weeks ago, they
taught a 4 hour class on NFPA70E and the CFR's related to it. They
stated the CFR's are performance standards that already require that
workers protect themselves, but the CFR's do not give specifics.
NFPA70E gives the specifics so if it is followed the CFR requirements
will be met for this area. They stated that an electrician receives
an electrical burn requiring medical treatment about once every hour
for an 8 hour day or 40 injuries per week (USA.) That is
significant. Accepting NFPA70E is going to take some time, but you
can be rest assured it will become an accepted practice as time goes
on.

Some basic rules are:
Only qualified persons should be working on electrical circuits. This
means they have received the training and have the experience to do
the work.
Work all circuits de-energized unless turning them off creates more of
a hazard than working them hot.
If you work them hot use the proper clothing and equipment to protect
yourself from the energized circuits.
This may require insulating the circuits from being contacted and
insulating yourself so you do not come in contact.
If you are working 480 volts hot, use a protective hood, insulated
gloves (certified at 5kv), proper fire resistant clothing and
insulated tools.
If you are working voltages greater than 480 volts you should have
specialized training for that work.

I have come very close to being seriously hurt by 480 volts twice in
my life and when you consider a 40 year work history, one is very
likely to get burned at least once in that time.
I have been lucky, and that is all there is to it. During both near
misses, I was in a hurry and did not take the proper precautions
because I was trying to get the job done.
Learning about NFPA70E is a big plus for electrical safety.

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