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#202038 07/11/11 09:31 PM
Joined: Apr 2008
Posts: 20
N
Member
Does anyone have any experience wiring gantry cranes? I have a crane to wire but don't agree with the installers method of connecting the load conductors to the buss bars feeding the rolling hoist. He wants to leave my 8x8x4 junction box, mounted at the top of one of the columns, with 4 individual #8 THHN conductors and connect them to the ends of the 4 buss bars.
Art 610.11B does seem to allow individual conductors for short lengths, but common sense says 480v wiring of this sort should be enclosed. Is this commonly done? I told the plant manager that after the crane guy hooked it up and tested it, I was going to lock it off until I modified it to what I felt was a safe installation. This hoist is above a injection molding machine and these conductors could easily be reached by mold changers working on the press. Thankfully, I have the blessings of the plant manager, but I am just trying to insure I am not crying wolf. Any insight would be appreciated
Thanks,
Dave

Joined: Mar 2004
Posts: 947
T
twh Offline
Member
Shouldn't you use a service head to switch to open wiring?

Joined: Jun 2004
Posts: 1,273
T
Member
A gantry crane NOT using DC?

Or is this DC forward and backwards?

Bus bars feeding a rolling load?

I've never seen that.


Tesla
Joined: Jan 2005
Posts: 5,316
Cat Servant
Member
I work in a plant filled with cranes ... and none of them are DC. Frequency drives and AC motors, every one.

Ditto for the "open" bussbars with some manner of moving contact. Only the 'cross' trolleys use cables in a flexible raceway; the main 'bridges' travel on 1/4-mile long rails; that's a bit long for any form of cable.

I've never looked at the connections between the bussbars and the feeders; let me see what I can find. As luck would have it, we're hanging some new ones this month.

Joined: Apr 2008
Posts: 20
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Member
Well, they hooked up the crane today. Sure enough they had me run my THHN conductors through a chase nipple in my J-box and leave then hang. They then took these individual conductors and hooked them to the ends of the 4 buss bars. It looks terrible. If these conductors were 30 feet in the air, I wouldn't feel so bad, but these conductors are no more than 12 feet over the floor, and anyone standing on the machine under the gantry can easily grab them. They swear its legal and I can't find any reason to argue short off "it may be legal but it sure isn't safe!"

Joined: Jul 2004
Posts: 9,672
Likes: 7
G
Member
If there are open bus bars right there, the safety issue isn't the THHN. I assume people just figure out not to touch the bus bars wink


Greg Fretwell
Joined: Jan 2005
Posts: 5,316
Cat Servant
Member
Yup, as I suspected ....

The feeders have their conduit connect to an open bracket. The wires exit the pipe and have crimp-on lugs that bolt directly to the bussbars. There are fiberboard separators between the bussbars at this point, so the lugs (and your wrench) can't strike another buss.

The crane bridge connects to the bussbars with spring-loaded copper shoes.

While the bussbars appear to be 'open,' it's actually somewhat difficult to actually touch them, either with your fingers or with a tool.

Joined: Sep 2005
Posts: 97
J
Member
we have crane busbars too, about 20ft up.

most are connected with 4 core armoured cable. it looks pretty shonky, isolator at ground level then the armoured cable within 12" of the busbars, stripped back and individual conductors connected to each of the three or four busbars.

As Reno says, its quite hard to touch the live part, they are shrouded and ours are carbon with carbon collectors, only about 1/4" opening to get your finger in

DC cranes are long gone, even before inverter drives. we have fluid couplings and direct motors


I took my time, I hurried up, The choice was mine, I didn't think enough
Joined: Sep 2002
Posts: 914
Likes: 1
N
Member
I remember one bridge crane where a weatherhead was used to transition from the EMT to connect to the crane busbars, it really did not look that bad.

Joined: Mar 2007
Posts: 101
M
Member
In the buildings I work on the conductors come right out of the conduit and bolt right to the the bus'. 480 volt 100 amp 3 phase.


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