More than one main disconnect / safety disconnect

[alger9]

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It is a machine in an industrial setting; the operator will need to semi-frequently lockout and enter the machine. Access to the main panel is difficult so it will have a second disconnect located near the front of the machine for lockout purposes. The FLA of the panel is 38amp. The power supply is 3ph 480V.

I know the basics of wiring more than one main disconnects. The disconnects must be in series, line and load side should be in different raceways. Now what I don’t know is the standards if any for fusing and locating your first disconnect. Ie do I locate the first disconnect in the series outside of the main panel and then run it to the main panel disconnect or should the first disconnect always be located in the main panel. Also should both disconnects be fused, or just fused after the first disconnect, or after the second disconnect.

 

[charlie b]

I do not understand. Why would you ever need more than one disconnect for a service? The NEC requires that every service have a means for disconnecting all ungrounded conductors. But it does not require that you have two of them. What situation are you describing?

 

[billsnuff]

I did a rural residence with a 200A disco on the pole even though the home had a 200A disco in the panel, meter to disco to home, no bond in panel. POCO requirement. Is this close to what you are doing? Is it residential?

 

[tomP]

I know the basics of wiring more than one main disconnects. The disconnects must be in series, line and load side should be in different raceways. Now what I don?t know is the standards if any for fusing and locating your first disconnect. Ie do I locate the first disconnect in the series outside of the main panel and then run it to the main panel disconnect or should the first disconnect always be located in the main panel. Also should both disconnects be fused, or just fused after the first disconnect, or after the second disconnect.

Are you speaking of an industrial setting where there are two disconnects in the line side conductors feeding a machine?

 

[al hildenbrand]

Alger9,

Your question, as I read it, is about disconnecting equipment, not service disconnects.

Perhaps you could offer a few specifics, such as the type(s) of equipment being disconnected?

 

[alger9]

More info

More info

It is a machine in an industrial setting; the operator will need to semi-frequently lockout and enter the machine. Access to the main panel is difficult so it will have a second disconnect located near the front of the machine for lockout purposes. The FLA of the panel is 38amp. The power supply is 3ph 480V.

 

[tomP]

I don't know that there are any standards to govern this application,
however as long as the circuit has an ocpd at its feed point I see no
problem with which switch is first.

Also I see no reason the remote switch would need to be fused.

These switches should be plainly marked as identical lockout points, IMHO.

 

[billsnuff]

alger9

alger9

I work in an industrial setting. Distribution is 480 3ph overhead buss with fused disco for each machine, marked and labeled. from there to the machine disco labeled E1, unfused, the to MCC which has an external disco labeled, E2 also unfused, then to isolation trans and back to MCC internal to MCCB. This is to comply with LOTO, within site rule (see NEC 100 In Sight definition) and the fact that we lose a phase from time to time and E1 must be disconnected to save the motors. I will not claim that this set up is 100% compliant as the factory was built in the 50's and we have several things that will not meet todays code but were compliant when installed.

 

[George Stolz]

I know the basics of wiring more than one main disconnects. The disconnects must be in series, line and load side should be in different raceways.

That is an urban legend - about the only time conductors passing through a disconnect can't use the same raceway to get to the disconnect are service conductors, 230.7.

Ie do I locate the first disconnect in the series outside of the main panel and then run it to the main panel disconnect or should the first disconnect always be located in the main panel.

This still confuses me, even with what you've added. Perhaps the others have answered this well enough, but I'm not clear on what you meant by this.

Also should both disconnects be fused, or just fused after the first disconnect, or after the second disconnect.

If the equipment specifically requires fusing in it's instructions, then the simplest way to achieve this is to install a fused disconnect at the equipment being served.

If the branch circuit's circuit breaker (which protects the conductors between the panelboard and the outlet) complies with the requirements for overcurrent protection that the machine may have, then a non-fused switch is acceptable.

See Article 404.

 

[dbaird]

NFPA 79 "Electrical Standard for Industrial Machinery" covers this in Chapters 5 and 6.

 

[VinceS]

I understand...

I understand...

As long as one of your disconnects is within NEC specified distance from your motor, the other can be placed in a location that has required working space around it. I have tended to group disconnects for ease of access to the operator, (AKA the person which destroys what you build). I never fuse these remote disconnects as the OCP is in the MCC bucket.

 

[petersonra]

I am not real sure why you would necessarily need a second disconnect to enter the machine, unless you mean physically crawling inside it. In that case there could well be other sources of energy that have to be dealt with.

 

[quogueelectric]

sounds like

sounds like

You want to install a 60 amp 480 volt unfused lockable safety switch for local service on this equipment. Do be aware That the control voltage may be from a second source and will not be capable of starting the equipment but may pose an electrocution hazard if someone mistakenly thinks all power is off

 

[tomP]

It is a machine in an industrial setting; the operator will need to semi-frequently lockout and enter the machine. Access to the main panel is difficult so it will have a second disconnect located near the front of the machine for lockout purposes. The FLA of the panel is 38amp. The power supply is 3ph 480V.

I agree there may and probably will be other energy sources to lockout however he didn't ask about lockout . He ask about which switch of the two in series should be first.
We have this several places where the main panel is on a balcony or not convenient to the machine.
We use this remote disconnect as the main panel lockout.
Are there other lockout points, yes, but they are more accessable.

 

[pfalcon]

Ouch - Bad Installation

Ouch - Bad Installation

*
It is a machine in an industrial setting; the operator will need to semi-frequently lockout and enter the machine. Access to the main panel is difficult so it will have a second disconnect located near the front of the machine for lockout purposes. The FLA of the panel is 38amp. The power supply is 3ph 480V.

I know the basics of wiring more than one main disconnects. The disconnects must be in series, line and load side should be in different raceways. Now what I don?t know is the standards if any for fusing and locating your first disconnect. Ie do I locate the first disconnect in the series outside of the main panel and then run it to the main panel disconnect or should the first disconnect always be located in the main panel. Also should both disconnects be fused, or just fused after the first disconnect, or after the second disconnect.

NFPA 79 "Electrical Standard for Industrial Machinery" covers this in Chapters 5 and 6.

The situation you are describing does not qualify the disconnect at the operator station as a machine disconnect. It cannot be used as a lockout point. See the chapters pointed to by dbaird.

A remote lockout point is only used when the disconnect cannot for practical purposes be located adjacent or on the control panel. Special restrictions apply.

What you are describing does not require fusing nor does it require the primary power to be brought to the disconnect. It does require a remote interlock kit that will trip the primary when the operator disconnect is pulled. After the operator is done; he removes his lock; he turns on the secondary disconnect at the operator station; then he turns on the primary disconnect at the control panel. Which sort of defeats the purpose for having a secondary disconnect at the operator station. The primary disconnect must remain tripped until manually restored.

Most machine tools require the removal of potential hazards before the operator may enter the machine. They do not explicitly require removal of electrical power. Even dropping the Estop circuit is more practical in virtually every case. Why are you going for a machine kill?