Bus duct re-torque

[MPdesign]

Bus duct re-torque

I know that older big panels can be taken apart and all connections checked (to solve hot spots shown in infra-red), but what about bus duct?

[inspector57]

I give, what is "bus duct"?

[MPdesign]

It is in non-residential work. When feeding electrical in say, a plant ceiling, or a building floor to floor; then instead of using conduit and wire, they sometimes use bus duct.

It is really copper bars in a metal case with attachment points every once in a while for disconnects (disconnects made for that particular bus duct only).

The best use of it is in a factory ceiling because they always get new equipment which needs different power needs - then they just change out the bus duct disconnect and run power down to the equipment... instead of... running new wire all the back to the panel. changing the breaker, demo'ing the old pipe and wire, etc...

I know - I know.. This is a residential forum mostly. But I like you guys better.

[Bill Kibbel]

Unless the conductor joints are welded, I'm pretty sure bolted splices are supposed to be regularly inspected and tightened when needed.

[Marc]

Bus duct re-torque

I know that older big panels can be taken apart and all connections checked (to solve hot spots shown in infra-red), but what about bus duct?

Sure, you can take them apart. When I worked at a forge plant, the company once expanded the production line and bought some used 1,000 amp 3 phase duct. My job was to take them apart, clean 'em and make sure they were still good for duty.

If you do it, get some manufacturer info on it first and follow the precautions religiously. We had a one that exploded, even though it looked fine to me, showering hundreds of sparks over a 30' wide circle on the forge floor.

You don't want any pointed surfaces on the buss, every energized surface must be smooth. After you re-torque, sometimes the socket will leave a sharp surface on the bolt head. Got to avoid that. Keep some extra bolts handy.

Bill may be right, I haven't seen the welded variety.

Marc

[Douglas Hansen]

For the last couple of decades, bus ducts typically have breakaway bolt heads, where the second bolt head snaps off at the proper torque. The only failures I have seen were instances where a connecting section wasn't fully seated prior to torquing the bolts.

[MPdesign]

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The problem does appear to be at the splice plate - in several locations - on the same side.

Perhaps that side had tension on it during installation causing poor seating?

What do you think Douglas?