How many grounds per ungrounded conductors

[transman2]

Have a Plc cabinet that is feeding 120V circuits out in the field to different devices such as pull switches, limit switches and over travel switches on a conveyor system. What does the code say on how many grounding conductors per ungrounded conductors. Looks like on this project very few grounds are being pulled in. I'm seeing 20+ hots with only 1 ground for example.

 

[Dennis Alwon]

I believe you are talking about grounded conductors (neutrals) and not grounding conductors-- Is that correct?

 

[Dennis Alwon]

If all the hots are on one, two or three phase and the loads are not overloading the breakers or the neutral then it may be compliant. You can have two hot conductors for one ungrounded conductor on single phase and 3 for 3 phase, however it may be wired that this is the way it is.

 

[Dennis Alwon]

Think of it as a hot and neutral going to a 10 gang switch box. That neutral could possibly carry all 10 switch legs .

 

[infinity]

You only need one EGC sized for the largest OCPD ahead of the circuit(s). If the raceway is metallic and qualifies as an EGC you don't need any wire type EGC's.

 

[AlexJ2406]

Article 250.122(F) States

Where conductors are run in parallel in multiple raceways or cables as permitted in 310.4, the equipment grounding conductors, where used, shall be run in parallel in each raceway or cable.

Then you size according to the ocpd protecting the cable/raceway.

This is for the egc, but not sure about the neutral. i actually was about to post the same question. I have a 3 phase system, using 5 multi-conductor 600MCM run in parallel per phase, but not sure how many is required for neutral. I sized the egc as stated above, but cant find the sizing or how many to use for neutral. Anyone??

 

[jumper]

Just to be clear here before answering.

You have 5 runs of pipe with 1 500MCM per phase in each pipe correct?

What size EGC do you have and what is the OCPD?

You will need a neutral in each pipe with the size based on the total imbalance of the feeder circuit divided by the number of cables, here 5.

 

[Smart $]

Have a Plc cabinet that is feeding 120V circuits out in the field to different devices such as pull switches, limit switches and over travel switches on a conveyor system. What does the code say on how many grounding conductors per ungrounded conductors. Looks like on this project very few grounds are being pulled in. I'm seeing 20+ hots with only 1 ground for example.

You only need one EGC sized for the largest OCPD ahead of the circuit(s). If the raceway is metallic and qualifies as an EGC you don't need any wire type EGC's.

Likely control, no actual load. In many cases, each "switch leg" is fused at a very low ampere rating... think DIN-rail terminal blocks with AGC-style fuses like old cars use to have. Usually run with 14ga control cable... but could use single conductor.

 

[Smart $]

Article 250.122(F) States

Where conductors are run in parallel in multiple raceways or cables as permitted in 310.4, the equipment grounding conductors, where used, shall be run in parallel in each raceway or cable.

Then you size according to the ocpd protecting the cable/raceway.

This is for the egc, but not sure about the neutral. i actually was about to post the same question. I have a 3 phase system, using 5 multi-conductor 600MCM run in parallel per phase, but not sure how many is required for neutral. I sized the egc as stated above, but cant find the sizing or how many to use for neutral. Anyone??

For paralleled conductors each cable has to have the same characteristics... which amounts to, if one cable has a neutral they all must.

Size at a minimun for the calculated load, taking reduction of 220.61 into consideration, but in no case smaller than 1/0 or the required EGC size.

 

[petersonra]

Have a Plc cabinet that is feeding 120V circuits out in the field to different devices such as pull switches, limit switches and over travel switches on a conveyor system. What does the code say on how many grounding conductors per ungrounded conductors. Looks like on this project very few grounds are being pulled in. I'm seeing 20+ hots with only 1 ground for example.

You are not generally required to have more than one (equipment) grounding conductor regardless of the number of conductors involved.

If you are using certain wiring methods such as EMT or rigid conduit, the EMT or conduit can serve as the EGC and no wire type EGC is required at all.

if you are referring to grounded conductors (e.g. - neutrals) you only have to pull a single neutral for each circuit. each circuit might have multiple wires involved.

 

[AlexJ2406]

5 cables total running parallel, each cable has 3 conductors. 5 parallel 3 conductor 600 MCM cable installed on a cable tray. OCPD is a 2000A CB, and for the EGC i used Table 250.122 and selected 250MCM.

Now, is article 250.122(F) saying i need an EGC in each cable mentioned above?

Thanks

 

[Smart $]

5 cables total running parallel, each cable has 3 conductors. 5 parallel 3 conductor 600 MCM cable installed on a cable tray. OCPD is a 2000A CB, and for the EGC i used Table 250.122 and selected 250MCM.

Now, is article 250.122(F) saying i need an EGC in each cable mentioned above?

Thanks

What Code cycle? 2011 below, highlighted text was added/changed:

(F) Conductors in Parallel. Where conductors are installed
in parallel in multiple raceways or cables as permitted in
310.10(H), the equipment grounding conductors, where used,
shall be installed in parallel in each raceway or cable. Where
conductors are installed in parallel in the same raceway, cable,
or cable tray as permitted in 310.10(H), a single equipment
grounding conductor shall be permitted. Equipment grounding
conductors installed in cable tray shall meet the minimum
requirements of 392.10(B)(1)(c).
Each equipment grounding conductor shall be sized in
compliance with 250.122.

PS: Service or feeder application?

 

[AlexJ2406]

Smart$, i guess it would help if i had the most up to date code cycle. I am using 2008.

This is for a feeder application though.

Thanks for the help.

 

[AlexJ2406]

Also a little help on what 392.10(B)(1)(c) states would be nice.

Thanks.

 

[Smart $]

Also a little help on what 392.10(B)(1)(c) states would be nice.

Thanks.

Sure...

(c) Single conductors used as equipment grounding conductors
shall be insulated, covered, or bare, and they shall be
4 AWG or larger.

 

[fmtjfw]

Have a Plc cabinet that is feeding 120V circuits out in the field to different devices such as pull switches, limit switches and over travel switches on a conveyor system. What does the code say on how many grounding conductors per ungrounded conductors. Looks like on this project very few grounds are being pulled in. I'm seeing 20+ hots with only 1 ground for example.

Looking at the original post, it appears to me that he is describing INPUTS to the PLC. If that is the case the single "ground" is the source for all the input devices and the 20 wires are the signals from the devices. The total current is probably measured in milliamps.

The only reason for multiple "ground" wires would be to avoid common mode interference.