Junction Box Materials

Yes. The replacement will be satisfactory, provided the requirements under Ex e for numbers of wires in terminals can be complied with.

.......and provided it has the same gas group and temperature class rating as the Ex d box that it is replacing.

Also look at the Ex e terminal box certificates provided with the boxes for more information (sometimes they have quite a bit including sizing design information).

Don't forget your power consumption / heat dissipation.

The Ex d box may contain ignition sources if relays or transformers are in it.

You MUST check all components in the box to ensure Ex e certification, as opposed to the Ex d box that may contain ignition sources.

Also all cable glands may have to be replaced, and check the porosity of your cables as barrier glands may be required.

Also, please be reminded the electricstatic effect for the JB surface, that means you have to request vendor to provide the anti-electricstatic box.

I have investigated one nighttime fire where a night photo of the blaze clearly had shown two Ex e composite boxes ablaze without any other fire nearby. i.e. there was no flash-over from the nearby main blaze to spontaneously ignite the composite boxes.

The conclusion was internal heat from two overloaded circuits (corroded switch connection points inside the boxes) reached a temperature above the autoignition point of the box material. 25 year old breakers had failed to protect the circuits.

Solutions were: SS boxes, new breakers, new cables, breaker test program, program for thermal imaging of connections.

So for the first time in my 35 year career I now check the autoignition and melting point of boxes in hazardous zones.

If those boxes were located in a hazardous zone I do hope those were Ex ed rated parts inside that Ex e box.

Are you able to provide more details here as this sort of thing is not supposed to happen unless the box was incorrectly installed, not maintained, operated in the wrong environment or incorrectly sized for the heat dissipation load (or combinations of the above)? I would be interested to know.

Hi Jack,

Yes, the existing JBs are Ex 'd' rated with cable terminals inside installed in Zone 1 and Zone 2 areas. These JBs are heavily corroded due to marrineenvironment poor maintenance program and I am not confident of their Ex integrity. Now I intend to replace them with Plastic Ex 'e' JBs (entire JB with all inside components) and would like to see your concerns if any.

Thank you all for helpful discussion

The insides were Ex d switches (hand Off Auto), but heat is heat, like from cables and dirty connections. I found dirty connections in other Ex d devices when I opened them up (corroded - sweating inside from humidity). Both boxes fed plastic cooling fan motors on equipment near the main fire, and the heat of the big blaze melted the fans. As the fans deformed and stuck to the fan guard, overcurrent set up and the breakers didn't open. Upon forensic disassembly the fan motors had locked rotors until fans were broken off the hub, then the rotor turned free with slightly melted fan bearing grease still OK. Heat on cables inside the Ex e boxes with Ex d fan control reached levels higher than the autoignition temp of the Ex e plastic boxes. Ignition !!! The photos (can't share sorry) clearly show two tiny flames at night on these boxes, 4 m away from the main blaze and protected from flash over heat by large pieces of equipment shielding them from the main blaze. And the two fan boxes that ignited were 3 meters apart from each other (mounted on two separate machines) so they are totally independent flames from each other, identical in size and shape (crescent shaped from cable just below box, engulfing box, and rolling over top of box). i.e. it was clearly self ignited from heat not directly related to the ambient heat outside the boxes.

Good question.

First of all, bear in mind that an Ex 'd' enclosure is designed to withstand certain internal explosions and pressures, while an Ex 'e' protection scheme means that apparatus producing arcs or sparks in normal service is not allowed to be located inside it. So, if your junction box has any type of thermal or sparking apparatus like switches or fuses, then you can't use an 'e' type box.

If the junction box is part of an approved device, such as being a part of a panel, motor, lighting fixture or whatever, then the answer is NO you can't replace it. Electrical equipment must comply with certain standards, and it is not legal to modify it in any way without the written consent of an accredited approval agency.

Either way, all electrical installations, especially in hazardous locations, must adhere to strict standards and regulations and must be inspected by a qualified person. I would suggest calling your local hydro authority (or whoever has the government mandate) and seeking their advice before doing anything.

Grae

Hi Graebeard,

Thanks for your detailed and useful discussion. I am going to follow your suggestion to consult local authority.

Good day

HHung.