HazLoc Headaches

bwat

EE
Location
East Coast
Occupation
EE
I'm only involved in classified area designs once every blue moon, so I'm rusty every time I look at one.

I have float switch in CID2 area and I just need the signal back to a control box in unclassified area. Float switch is explosion proof.

Concept that I'm evaluating:
XP Float switch through side wall of tank
Float switch to junction box mounted on side wall of tank using flex conduit and the wire supplied with float switch.. Probably LFMC.. Per 501.10(B)(2)
- Fittings are listed but just general purpose
- No seals in LFMC
Junction box is just general purpose per 501.10(B)(4) and 500.8(B)(3). No special markings or classifications.
From junction box to unclassified area (therefore crossing boundary) control box using MC per 501.10(B)(1)(5)
- Fittings are listed but just general purpose
The MC cable may or may not need a seal depending on exact cable per 501.15(E)(2) through 501.15(E)(4) . The junction box is not required to be explosion proof so a seal is only needed if it is a cable as 501.15(E)(4). i.e. a seal will not be needed from 501.15(E)(1)

So potentially this:
(Float)--(LFMC)--(JB)--(MC)---(Ctrl Pnl)
where the boundary from CID2 to unclassified is during the MC run

Anything wrong here?

2017 NEC
 

nhee2

Senior Member
Location
NH
if the float switch is arcing/sparking, and reliant on the explosion-proof enclosure, you'd need an XP seal at the switch, per 501.15(B)(1). Although sometimes those switches are potted with pigtails, then likely does not require a seal.

Is the inside of the tank classified?
 

bwat

EE
Location
East Coast
Occupation
EE
Good to note. I believe the switch is potted with pigtails, but worth checking.

Inside of tank is same as immediately outside. CID2
 

bwat

EE
Location
East Coast
Occupation
EE
I don't do this stuff on a regular basis but the ones I've seen all used an intrinsically safe circuit for the level switch(es). But keep in mind my sample size is pretty low.
Thanks, but to do that you would need a separate IS barrier in control panel and still have the same concerns with cabling and conduit, correct? It would be difference of swapping out the switch for IS capable one and adding IS barrier in control panel, or just use the XP switch.

(if I understand correctly... and I certainly have doubts here which is why I'm asking... also, customer has selected the XP switch)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Thanks, but to do that you would need a separate IS barrier in control panel and still have the same concerns with cabling and conduit, correct? It would be difference of swapping out the switch for IS capable one and adding IS barrier in control panel, or just use the XP switch.

(if I understand correctly... and I certainly have doubts here which is why I'm asking... also, customer has selected the XP switch)
There are different wiring method options for IS circuits. The switch could remain an XP device even if the circuit was IS.

You are right about needing to add an IS barrier, and that at least some of the cabling and conduit concerns would remain.

I think you still need a boundary seal.
 

bwat

EE
Location
East Coast
Occupation
EE
I think you still need a boundary seal.
Even with my original setup? 501.15(E)(2) through 501.15(E)(4) are not that easy to navigate, but it seems like it just depends which cable is used. If I specify MC-HL, for example, no boundary seal would be needed from what I can tell.
 
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