Hello I am confused on a few things regarding the grounding for field devices in this case. For an overview of the Conveyor system it has
8 x 30 amp 480VAC circuits coming out of panel to 4 pole multi conductor cable with a ground wire
3 X 30 amp 120VAC circuits coming out of a panel to 3 pole multi conductor cable with a ground wire.
The 480 VAC feed VFDS along the line.
The 120 VAC feed field mounted 24vdc Power supplys which feed 24vdc field devices ( IO Blocks ETC ).
Our plan based on my knowledge is to Install UGB on the line where all of the gnd connections for the field devices will be brought back to in their appropriate size Mainly 10 AWG for the 120 VAC and 480VAC then 14 AWG for the 24vdc based on the 8 amp fuse in the power supply module.
All of the different UGBS will connect to the wiretray using approved connection methods. For the continuous runs of cable tray that meet by the panel a single GND wire will be connected at the panel for the sections that are not continuous a single cable will run back to the panel individually.
Based on the cross section of the wire tray at .42 sq in (Steel) and table NEC 392.7(B). it is rated to be used as a EGC for up to a 100amp OCPD.
There is a chart in section 392.60 “Grounding and Bonding” which states the “maximum fuse ampere rating, circuit breaker ampere trip setting, or circuit breaker protective relay ampere trip setting for ground fault protection of any circuit in the cable tray system” based on the minimum cross-sectional area of the tray.
Our largest OCPD is 30 amp this should work according to my understanding.
Am I overlooking something here?
Thank you for your help.
8 x 30 amp 480VAC circuits coming out of panel to 4 pole multi conductor cable with a ground wire
3 X 30 amp 120VAC circuits coming out of a panel to 3 pole multi conductor cable with a ground wire.
The 480 VAC feed VFDS along the line.
The 120 VAC feed field mounted 24vdc Power supplys which feed 24vdc field devices ( IO Blocks ETC ).
Our plan based on my knowledge is to Install UGB on the line where all of the gnd connections for the field devices will be brought back to in their appropriate size Mainly 10 AWG for the 120 VAC and 480VAC then 14 AWG for the 24vdc based on the 8 amp fuse in the power supply module.
All of the different UGBS will connect to the wiretray using approved connection methods. For the continuous runs of cable tray that meet by the panel a single GND wire will be connected at the panel for the sections that are not continuous a single cable will run back to the panel individually.
Based on the cross section of the wire tray at .42 sq in (Steel) and table NEC 392.7(B). it is rated to be used as a EGC for up to a 100amp OCPD.
There is a chart in section 392.60 “Grounding and Bonding” which states the “maximum fuse ampere rating, circuit breaker ampere trip setting, or circuit breaker protective relay ampere trip setting for ground fault protection of any circuit in the cable tray system” based on the minimum cross-sectional area of the tray.
Our largest OCPD is 30 amp this should work according to my understanding.
Am I overlooking something here?
Thank you for your help.
Last edited: