Grounding of industrial control panel

mhismail

Member
Join Date
Mar 2016
Location
egypt
Posts
30
Hi,

I have an industrial control panel with the following:

dimensions: 600 x 600 x 250mm
Panel feeder : #14 AWG , MC cable PVC-coated , supplied from a main power cabinet (5m away from our panel) ,380 v ac 3-phase , 4-wire : L1,2,3 & N
DC circuits inside : 24 vdc/5A power supply and another 24 vdc/20A power supply
Overcurrent devices 3A (at supply side of first power supply) & 5A (at supply side of second power supply)
the system is ungrounded (the MC feeder cable has NO grounding wire (green/yellow) )

My Questions:
----------------

1) I should refer to Table 250.122 to get the grounding conductor size for each equipment separately (size of each power supply bonding jumper by the of rated current of the upstream circuit breakers mentioned above) , is that correct?

2) what about grounding panel ? I know that all the jumpers will be bonded to the panel-board , then there should be some conductor or rod coming through the panel and fixed to the earth under the panel , correct? how to size that? what section of The NEC mentioned that ?

Thank you in advance
 
What country is this panel installed in?

The NEC has jurisdiction in the United States of America.

You need to comply with local standards and governing bodies.
 
What country is this panel installed in?

The NEC has jurisdiction in the United States of America.

You need to comply with local standards and governing bodies.

As an answer to your question , it is Egypt

but the NEC is far far more than just a local standard for the USA. It is truly an international code.It is also known that most of the world follow NEC or IEC.

In Egypt NEC & NFPA in general is of course accepted.

About my questions in the main post ,Do you have answers?

Thanks for your reply
 
Hi,

I have an industrial control panel with the following:

dimensions: 600 x 600 x 250mm
Panel feeder : #14 AWG , MC cable PVC-coated , supplied from a main power cabinet (5m away from our panel) ,380 v ac 3-phase , 4-wire : L1,2,3 & N
DC circuits inside : 24 vdc/5A power supply and another 24 vdc/20A power supply
Overcurrent devices 3A (at supply side of first power supply) & 5A (at supply side of second power supply)
the system is ungrounded (the MC feeder cable has NO grounding wire (green/yellow) )

My Questions:
----------------

1) I should refer to Table 250.122 to get the grounding conductor size for each equipment separately (size of each power supply bonding jumper by the of rated current of the upstream circuit breakers mentioned above) , is that correct?

2) what about grounding panel ? I know that all the jumpers will be bonded to the panel-board , then there should be some conductor or rod coming through the panel and fixed to the earth under the panel , correct? how to size that? what section of The NEC mentioned that ?

Thank you in advance
1) You are probably over thinking this a bit. Most control circuits will be run in 14ga wire, so 14ga grounding conductors is fine (which is what 250.122 says anyway) and for anything larger yes, you can use that. technically though, the NEC is not a standard for building a control panel, it is a standard for INSTALLING stuff. NFPA 79 and UL 508A are standards for building control panels. In this regard though, the info in 250.122 is the same anyway.


2) Again, in building the PANEL, you do not concern yourself with how it is grounded in the field, that is the purview of the installing electrician. In general though, you would NOT run a ground rod at the panel site, unless that panel is also the "Service Entrance" from the utility feed. If it is being fed FROM another system at the site, then you would run an EGC (Equipment Grounding Conductor) from the source to this panel, sized per 250.122 also.
 
"the system is ungrounded (the MC feeder cable has NO grounding wire (green/yellow)"

Does this MC cable have a metal jacket? Does this MC cable have a bare/un-insulated conductor?

It is common, in my experience (US only) that MC cable does not have a green, or green/yellow ground conductor. With approved attachment fittings, the metal jacket and the bare conductor serve as the ground conductor. Is your control panel metal? The ground would be 'bonded' through the approved/listed MC attachment fitting, to the control panel.
 
1) You are probably over thinking this a bit. Most control circuits will be run in 14ga wire, so 14ga grounding conductors is fine (which is what 250.122 says anyway) and for anything larger yes, you can use that. technically though, the NEC is not a standard for building a control panel, it is a standard for INSTALLING stuff. NFPA 79 and UL 508A are standards for building control panels. In this regard though, the info in 250.122 is the same anyway.


2) Again, in building the PANEL, you do not concern yourself with how it is grounded in the field, that is the purview of the installing electrician. In general though, you would NOT run a ground rod at the panel site, unless that panel is also the "Service Entrance" from the utility feed. If it is being fed FROM another system at the site, then you would run an EGC (Equipment Grounding Conductor) from the source to this panel, sized per 250.122 also.


(1) You are correct , all my grounding conductors are #14awg wires. I figured that late after referring to the table. I don't mean to overthink , I just prefer to have some reference before sizing electrical parts.
And yes you are correct that NEC isn't for panels , I read both NFPA 79 & NEC (not all chapters of NEC) but some times NEC gives more details like motor control panels. Chapter 8 in NFPA 79 (grounding) is only about 3 pages and mentioned nothing about grounding the panel itself so I tried to look for any guidelines in the NEC.

(2) Well , It is not the service entrance. I know it is the scope of the installing electrician , but I just wanted to have some figure instead of just accepting anything he installs.
 
"the system is ungrounded (the MC feeder cable has NO grounding wire (green/yellow)"

Does this MC cable have a metal jacket? Does this MC cable have a bare/un-insulated conductor?

It is common, in my experience (US only) that MC cable does not have a green, or green/yellow ground conductor. With approved attachment fittings, the metal jacket and the bare conductor serve as the ground conductor. Is your control panel metal? The ground would be 'bonded' through the approved/listed MC attachment fitting, to the control panel.

well , the cable has galvanized steel interlocked armor and pvc jacket . And yes it has a bare copper conductor.The cable is direct buried.

so you suggest that the bare conductor be bonded to the enclosure body (which is metal) through the fitting , correct? then would the fault current (when occur) flow to the earth since the cable is direct buried despite the pvc jacket ? or should the bare conductor be connected to something else at the other side (main supply 380v panel) ?
 
You must connect a ground wire to the earth inside the main supply cabinet, from this you must have a grounding wire of at least half the size of normal conductors. with a minimum of 16 mm. etc. every equipment must be connected to ground, also, the doors of the cabinet.
 

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