Crane Disconnects

[heath harry]

We have two separate cranes in separate bays being fed from 480 volt switchgear located in an electric room. We showed a 2000 amp and 1600 amp disconnect located in each bay in line of sight from the cranes. Article 610.31 of the NEC states as follows:

610.31 Runway Conductor Disconnecting Means. A disconnecting means that has a continuous ampere rating not less than that computed in 610.14(E) and (F) shall be provided between the runway contact conductors and the power supply. Such disconnecting means shall consist of a motor-circuit switch, circuit breaker, or molded case switch. This disconnecting means shall be as follows:
(1) Readily accessible and operable from the ground or floor level.
(2) Capable of being locked in the open position.
(3) Open all ungrounded conductors simultaneously.
(4) Placed within view of the runway contact conductors.

Does a Pringle disconnect Switch meet this code article since it has to consist of a motor-circuit switch, circuit breaker, or molded case switch. If not what type of switch should be installed. If the breaker in the electric room is lockable does a disconnect even have to be installed?

[ August 11, 2003, 03:38 PM: Message edited by: heath harry ]

 

[heath harry]

Re: Crane Disconnects

Is there anybody out there that may have some input on this issue.

 

[jim dungar]

Re: Crane Disconnects

I believe, the Pringle "bolted pressure" switch would meet the need as it is a motor-circuit switch.

The padlockable circuit breaker, in the switchgear, would only be acceptable if it meets the "in view" requirement of 610.31(4). Line of sight and not more than 50' distant are both requirements to be "in view".

 

[heath harry]

Re: Crane Disconnects

Thanks Jim, exactly what I thought. This brings another question to mind...what precisely is the definition of a motor-circuit switch?

 

[don_resqcapt19]

Re: Crane Disconnects

Jim,
Are you saying that "in view" is the same as "in sight"? I think that the code panel made a choice to use "in view" in place of "in sight" because of the lenght of the conductor rails on many overhead cranes is much greater than 50'. 610.31(4) appears to require that the disconnect be place where it can be "viewed" from any point along the conductor rails. Even "in view" is pushing it for long runs.
Don

 

[heath harry]

Re: Crane Disconnects

I agree with the previous post. These bays are also 90 feet in the air thus it is impossible to make the disconnect accessible and within 50 feet.

 

[jim dungar]

Re: Crane Disconnects

Don,
You may be right, but...

The definition for "IN SIGHT FROM" has several examples and the phrase "and so forth", which I interpreted to include "in view of". I would start my distance measurement from the electrical start of the conductor bars.

Heath Harry,

My interpretation of motor-circuit switch is one that is rated for making and breaking motor power circuits (i.e. has a horsepower rating).

[ August 12, 2003, 04:25 PM: Message edited by: jim dungar ]

 

[don_resqcapt19]

Re: Crane Disconnects

Jim,
So in this case with the crane rails 90' above the floor the disconnect would have to be 40' above the floor. Not very easy to get to.
Don

 

[jim dungar]

Re: Crane Disconnects

A crane with rails 90' in the air is also "Not very easy to get to".

 

[don_resqcapt19]

Re: Crane Disconnects

Jim,
Many of those cranes are operated by radio control from the ground or in a cab on the crane. Where would the code required disconnect fot the crane rails be placed in this type of installation?
Don

 

[heath harry]

Re: Crane Disconnects

These are radio controlled cranes, but the disconnect is not meant to protect the operator, it is intended to protect the maintenance people working on the crane or working on equipment the crane services.

The question becomes whether a disconnect needs to be installed accessibly within view, even though it can't be within 15m, or will the breaker suffice that is in an electric room.


If proper lock-out tag-out procedures are used all maintenance work could be performed by locking the crane out in the electrical room. If work is being performed on crane, or even near the hot rails, while the crane is hot it would be safer to have the disconnect switch placed in view.

 

[don_resqcapt19]

Re: Crane Disconnects

Harry,
I can't see where the lockable breaker in the electrical room can comply with the rule in 610.31. The real questions is: Does "in view" mean the same as "in sight"? Are the conductor rails fed at multipel points along the rail? If so where would the disconnect be placed?
Don

 

[heath harry]

Re: Crane Disconnects

I would like to thank everybody for their input on this issue. It is good to see you have a place where you can receive other people?s input and interpretations on such issues.

I went directly to the NFPA through our corporate membership to receive an interpretation. I was told a disconnect switch is required.

Again I would like to thank everybody for their input.