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#209562 - 04/09/13 09:57 AM what PPE is required for a 24 volt circut
rapture Offline
New Member
Registered: 04/09/13
Posts: 1
Loc: Arkansas USA
what PPE is required for calabrating a 24 volt i/p transmitter circut in a class 1 division 2 area other than fr clothing
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#209568 - 04/09/13 04:36 PM Re: what PPE is required for a 24 volt circut [Re: rapture]
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6833
Loc: Brick, NJ USA
Rapture:
First...Welcome to ECN from one of the 'Jersey Guys'

I had a few brief minutes earlier and looked, but could not find any response to your inquiry.

Be patient, someone may have some input
_________________________
John
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#209587 - 04/10/13 09:36 AM Re: what PPE is required for a 24 volt circut [Re: rapture]
JBD Offline
Member
Registered: 07/12/01
Posts: 599
Loc: WI, USA
The reality is, there is no official list. Each company needs do decide what is appropriate for their work environment.
If your are using the 'task tables' in NFPA70E, then there is a list of PPE based on hazard risk categories. Many companies take the data from a study and work the lookup table backwards as their means of adopting the 70E clothing tables.

NFPA70E does not address voltages below 50V. It appears they have gone out of their way, in particular, to ignore 24V and less.
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#209588 - 04/10/13 10:43 AM Re: what PPE is required for a 24 volt circut [Re: rapture]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9066
Loc: Estero,Fl,usa
The problem in a C1D2 is not arc flash, it is arc "kaboom".
De energize the circuit or wear a "Hurt Locker" bomb suit if you think vapors are present in combustible concentrations.
Div 2 does mean it "may" contain vapors if something else bad is going on. (spill, leak, ventilation failure etc).
_________________________
Greg Fretwell
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#209591 - 04/10/13 11:55 AM Re: what PPE is required for a 24 volt circut [Re: rapture]
mikesh Offline
Member
Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
There is no PPR for the energy level of instramentation transformers but igniting a flammable vapour can kill you too and that is not arc Flash but flash fire. Your electrical PPR could offer lots of flame resistance but they are rated differently. A lot of early FR was sold as arc flash protection but things like pocket slashes are acting differently in a fire as opposed to an arc flash or Blast.
If the transformer is intrinsically safe output then in theory you can short the wires in an explosive atmosphere without igniting the gas and there is no possibility of an arc. Now if you are installing the transformer into a panel then PPR is coming into play.
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#209640 - 04/14/13 04:37 PM Re: what PPE is required for a 24 volt circut [Re: rapture]
mjolnir Offline
New Member
Registered: 06/21/09
Posts: 1
Loc: Suffolk County NY
I don't think it's an issue of PPE, but an issue is confirming atmosphere in area prior to removing cap on XMTR normally with labeling stating something to the same effect. Generally same rules associated with a hot work permit for the area in question apply. Any work location having the this type of area in should have a relatively well outlined procedure for the work, including but not limited to the monitoring of atmosphere for LEL and the work area in a condition that would not allow for an unexpected change in the atmosphere (Tag Out).

Hope that helps.

Keith
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#209700 - 04/18/13 08:13 PM Re: what PPE is required for a 24 volt circut [Re: rapture]
mikethebull Offline
Member
Registered: 03/18/07
Posts: 101
Loc: Rhode Island
It was my understanding that no PPE was required for 240/120 volts and below. I least that is what I read in NFPA 70E.
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#209706 - 04/19/13 08:31 AM Re: what PPE is required for a 24 volt circut [Re: mikethebull]
JBD Offline
Member
Registered: 07/12/01
Posts: 599
Loc: WI, USA
Originally Posted By mikethebull
It was my understanding that no PPE was required for 240/120 volts and below. I least that is what I read in NFPA 70E.


PPE is always required, when the system is >50V.

A specific arc flash study is not required by NFPA70E for certain systems (e.g. <240V fed by a 'small transformer')

There is no industry accepted method for performing arc flash calculations for single phase circuits.

No study does not mean no PPE.

Use the NFPA70E task tables.
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#209707 - 04/19/13 12:05 PM Re: what PPE is required for a 24 volt circut [Re: JBD]
mikesh Offline
Member
Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
Sure but PPE for some energy levels is a cotton shirt and blue jeans with safety glasses and gloves. In this case the circuit is under 50 volts and very low energy. In fact if it is an intrinsically safe output you could short the wires in an explosive atmoshpere without an explosion hazard. So PPE for a hazardous location might not be for an electrical fault but a gas explosion. Your arc flash gear may have a flame protection rating too.
The Canadian standard written from 70E puts the PPE for a single phase 120/240 volt service at a 0 which translates to denim or other non-synthetic clothing. At these levels there is no real ARC but a fault could make a lot of sparks and molten metal. In theory the voltage is too low to sustain an arc in the air.

Originally Posted By JBD
Originally Posted By mikethebull
It was my understanding that no PPE was required for 240/120 volts and below. I least that is what I read in NFPA 70E.


PPE is always required, when the system is >50V.

A specific arc flash study is not required by NFPA70E for certain systems (e.g. <240V fed by a 'small transformer')

There is no industry accepted method for performing arc flash calculations for single phase circuits.

No study does not mean no PPE.

Use the NFPA70E task tables.
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#209711 - 04/19/13 04:58 PM Re: what PPE is required for a 24 volt circut [Re: rapture]
Tesla Offline
Member
Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
My truck battery is 12VDC -- it throws arcs to beat the band.

DC arc welders use 24-36VDC -- depending -- so you can't assume that a 24VDC system can't spark.

You're just assuming that there is no battery back-up in the system -- and that the power supply is feeble. Even so, they can STILL spark.

In an explosive atmosphere - it just takes the one spark.

Virtually all fire alarm circuits will have battery back-up.

ANY critical control circuit is going to have battery back-up -- usually a serious lead-acid gell battery.

The mere selection of 12VDC or 24VDC ( instead of 24VAC ) makes one assume that the control circuit has a battery back-up.

It's kaboom every time. I've seen battery tops blown of by sparking jumper cables -- all at 14VDC.

Intrinsically safe circuits stay below 3VDC, not 24VDC.
_________________________
Tesla
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