Can a disconnect switch be installed at the bottom of the subpanel and under/below all control components/circuits?

HP19783

Member
Location
USA
Occupation
Learner
Can a disconnect switch be installed at the bottom of the subpanel and under/below all control components/circuits?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The details matter, but in general where you choose to locate a disconnect is up to you. I have been known to install a main MCCB at the bottom of a control panel and reverse feed it because the incoming feeder is underground and it will make it a lot easier for the electrician to hook it up.

I will say that most disconnect switches are not labeled to allow them to be reverse fed, while many MCCBs are labeled to be reverse fed.
 

HP19783

Member
Location
USA
Occupation
Learner
The details matter, but in general where you choose to locate a disconnect is up to you. I have been known to install a main MCCB at the bottom of a control panel and reverse feed it because the incoming feeder is underground and it will make it a lot easier for the electrician to hook it up.

I will say that most disconnect switches are not labeled to allow them to be reverse fed, while many MCCBs are labeled to be reverse fed.
Sorry to mention that it's not MCCB. It is 460 VAC-3 phase fusible disconnect rotary switch.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Doesn't matter. Why do you think it's a problem?

Are you talking about facing the switch downwards on the bottom of the cabinet? Or just one enclosure below another?
 

HP19783

Member
Location
USA
Occupation
Learner
Doesn't matter. Why do you think it's a problem?

Are you talking about facing the switch downwards on the bottom of the cabinet? Or just one enclosure below another?
1. the disconnect switch (DS) is not facing down. It's installed on the bottom of the panel and all control devices are directly above it.
2. Everything is in (1) enclosure.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The switch is not enclosed as MCCB and its leads are more exposed. If it's installed on the bottom, it creates more hazard if something above it dropped on the lines.
How would dropping something on a live wire at the bottom of the cabinet be more hazardous than dropping it on something live at the top of the cabinet.

No one is supposed to be working in the cabinet with the power on anyway, except in some rare cases, and in those cases appropriate PPE would be required to prevent injury.
 

HP19783

Member
Location
USA
Occupation
Learner
I think I don't clearly details my concerns. If DS is installed on the bottom with all control components such as controller, VFD, sensors' cables above it, these items might be got loose and dropped on the DS due to installations, vibrations during operations, etc. This cabinet controls a big motor and mounted on the same frame/house with the motor.
 

jap

Senior Member
I never understood the point of an integral disconnecting means.

There will always be power available on the line side of the control cabinet disconnect regardless of whether the disconnect is off unless you lock out the source.

Much like line side power to a shunt trip breaker on an MDP fed directly from a utility transformer.

Thousands of control cabinets are set up this way.

The disconnecting means in the control panel itself does not disconnect the power inside the enclosure.

JAP>
 

HP19783

Member
Location
USA
Occupation
Learner
I suppose it is possible that something might drop onto the switch. But if something came loose and something other than the switch was under it you would have the same problem.
The difference is DS have 460VAC, while others have either 24VDC/120VAC. Which one cause more serious hazards?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The difference is DS have 460VAC, while others have either 24VDC/120VAC. Which one cause more serious hazards?
If the DS has 480 VAC on it, there is a good chance other things in the cabinet also do.

The thing is that trying to make stuff so you think it is "safe" to work in the cabinet with the power on is how people get themselves killed. It is inherently unsafe to work on energized equipment, especially without proper PPE.
 

jap

Senior Member
Just as anything else, most of the hidden dangers are dependent on the caliber of the electrician doing the actual wiring.

JAP>
 
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