Instrument and Safety Grounding Practice 1

[DM2]

Can someone point me to where I might find requirements, recommendations, and best practice stuff, for both "Instrument" and "Safety" grounding?

I've been trying to find out things like what size of ground wire to use in a control panel, where 10 or so, 24 VDC instrument shields terminate on DIN rail mounted terminal blocks and other issues.

I'm not having any luck with my search, and I'm not sure if this is the right form to post in. I did a search under "Engineering Codes, Standards & Certifications" from "Instrument Ground" but came up empty.

Sure would like some recommendations.

Regards

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[davidbeach]

Since you posted in the IEEE forum, I'd suggest you start with the IEEE Green Book.

 

[dbaird]

I am attaching an "Industrial Automation Wiring" guidelines for your review.

You might want to move your post to "Measurement & control instrumentation engineering" for more replies.



David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[DRWeig]

Or, since you mention "control panel," you might want to invest in a copy of UL 508A.

Good on ya,

Goober Dave

 

[DM2]

UL 508A doesn't apply to Fire Panels. Have a read through the "Scope" information on the standard.

http://ulstandardsinfonet.ul.com/scopes/0508a.html

Section 1.6.2

regards

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[DM2]

I'm sorry...disregard my "UL 508A" post...

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[dpc]

If it's a fire panel, it would be good to indicate this - it will improve the responses you get.

 

[DM2]

This is a "Fire & Gas" panel, however the instrument grounding, I would think, would be similar to that required for a PLC.

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[REDDOG]

508A Still Applies From the UL White Book "NITW.GuideInfo
Industrial Control Panels.
Industrial control panels marked "Flame Control Panel" on the unit nameplate contain controls for fossil fuel-burning equipment, such as incinerators, kilns, and drying ovens, intended for industrial applications. These control panels may additionally contain controls for other loads."

 

[DM2]

REDDOG,
This panel isn't marked "Flame Control Panel", it's marked "Fire Panel" and has nothing to do with controls of the items you mentioned.

It controls and monitors Smoke Detectors, Flame Detectors, etc.


Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[EEJaime]

"Fire Panel", "Fire and Gas Panel", "Control Panel"? Which is it? These are vastly different things in most cases. If it is a Fire Alarm Control Panel that monitors "Smoke Detectors, Flame Detectors", it should be something that is State Fire Marshall listed, (assuming you are in the states), so it will have a panel/equipment grounding terminal or bus that is part of that approved assembly. If it is something that is custom manufactured and these Smoke and Flame detectors are some kind of process equipment and not a Fire/Life Safety issue, then the ground will be defined by whatever standard it is designed under. For low voltage instrumentation I would expect that a standard sized equipment grounding conductor for the included power supplies/transformers in the panel would suffice, but without more information , I don't know how to provide better information.
Regards,
Jim Murillo

 

[stookeyfpe]

You need to review NFPA 72, National Fire Alarm Code. It contains all the requirements you're wanting for a fire alarm control unit, which is what your device is termed as.

 

[JLSeagull]

Significant documents include the fire and gas panel manufacturer's recommendations and the National Electrical Code article 250.

For a solidly grounded system, assume that we have a large 480 Volt 3 phase UPS. We would likely have an isolation transformer. The ground on the Y would be tied to a ground rod. That rod would tie to the ground grid.

Often with a typical DCS the manufacturer would recommend a safety ground on the cabinets etc. tied to the grid at another rod. That rod too would be tied to the grid. Shield grounds might be tied to the same rod as the cabinet safety grounds. Another isolated ground would apply to the power supply common, often the 24 Vdc negative. Consider the panel vendor recommendations closely. Another issue would apply of the system includes intrinsic safety barriers as the barriers must be isolated from the safety grounds etc. and tied to the grid. Usually a separate rod is used for each type ground. Additonal rods may be required to assure a low resistance ground. For intrinsic safety the requirement is better than one ohm earth resistance. Then all of the rods ... everything is tied to the grid. I don't think that the fire and gas manufacturer's recommendations will be far from these suggestions.

 

[kontiki99]

I recently ran across SAE ARP1870 Aerospace Systems Electrical Bonding and Grounding for Electromagnetic Compatibility and Safety

It may not target your specific application. Possibly it's overkill. It's got some good data.

 

[DM2]

Kontiki99,
Thanks for the information...now if I had access to the document. I purchased a copy of a PIP document for $125.00 dated 1999 (I should have known) but the document was so outdated it wasn't funny.

With regard to the manufacturers, their documentation is extremely lacking.

With regard to the reference by stookeyfpe, to NFPA 72, there is only references to other standards such as NFPA 70.

One question I have is, if there are 12 instruments, all 24 VDC, is there a method or guideline for determining the ground wire size between these and the instrument ground buss bar?

Maybe a rule of thumb or something?

Regards,
Dan Marr

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[kontiki99]

This document discusses design requirements, fault current vs impedance, disimilar metals, frequency, surface prep, atttachment methods etc. It is dated 1999.

I've been on the lookout for wiring, shielding, bonding, info related to aviation lately. I think ARP 1870 is a good comprehensive presentation on bonding. Maybe something has superceded it, I don't know.

Were seeing MIL specs for a lot of aviation topics cutting over to SAE. I'm just trying to understand the resources that are out there myself.