fire pump grounding

Fire pump wiring is a separate unique subsection in NFPA 70 electric codes. (typical US wiring standards) This is because critical use of the pump occurs only during crisis conditions. Because of this I strongly urge you to refer to a qualified engineer and/or building code inspector.

What I can understand you are trying to do is to provide protective earth connection to your fire water pump metal parts. there is no problem to ground your fire water pump metal parts to your earthing grid if the earthing grid in question is not used also to ground the supply transformer neutral in a standard IEE TT system. this is to say that your neutral earthing in any installation must be electrically seperated from your PERSONNEL Protective Earthing grid.

Try see that your transformer neutral earthing and the protective erthing grid are electrically seprarated as a first. Ground then your fire water pump metal parts, including pump body, electric motor earth terminal, diesel engine metal parts etc, bond them firmly to the general "protectiove earthing grid" and will be safe. Note then that you have only this problem in a TT system. In the TNS system, you dont have this problem and any earthing found in the TNS will then do for personnel protective earthing use because in the TNS, no neutral earthing is required. the installation uses custom made lighting transformers for the LV and single phase load demands.

Concerning the NFPA codes, its applications are better appreciated in the specification of fire water pumps (eg max delivery pressure ratings to be encountered for personnel safety and the type of prime mover -electric motor or diesel engine). In many critical applications diesel prime movers are prefered to gunantee availability and to assuage the fears expresed when fighting fires of electrical origin since this require general installation outage. It does not however replace nor it is a substitute for the IEE regulations when it comes to procedures required for providing personnel protective earthing in installations viz-a-viz the installation designation TT/TNS/TNC etc.

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from Percy

I love how people who admit that they don't know what a standard states can still render an opinion. NFPA 70 is specifically the National Electrical Code (NEC) used in many municipalities in the United States. You can wire up your motor any way you want and it may succeed in pushing water. But unless you can prove compliance with your location's standards you are taking a risk.

The NFPA is NOT a code unless it is specifically adopted by the local governing authority and it is enforced by the AHJ (Authority Having Jurisdiction).

Several good suggestions are given here, but the safest route is to calmly discuss with the local AHJ, usually a fire inspector, and discuss how what you are proposing will protect public and fire-fighter safety. A calm discussion with some give and take will usually result in an acceptable solution.

Exactly my point. Contact your local authority how all wiring to your fire pump should be done. The NFPA 70 codes are NOT the final authority, your local authority has jurisdiction. Many locations do follow NFPA 70 and the four pages of code in Article 695 on Fire Pumps(not the sole pertinent section but the dominant one.) Wiring of emergency systems should not be decided by any anonymous committees. Even calm friendly committees like this one. CONTACT AN AUTHORIZED PROFESSIONAL!

LOL, I love the fact that you two are having a spat over the NEC and AHJs and State codes etc., neither of you seemed to notice that the OP is in Qatar!

thaks for your detailed answer but i have little bit confusion,in my case our distribution trf sec is 3phase+n with ct which is solidly grounded to GROUNDING GRID.Now you r saying that TNS system no neutral earthing is required but in our case neutral is equiped with ct to operate earth fault relay

what i understand in TNC PE conductor and neutral conductor is same

in TNS system PE and neutral is separate but your case u said that NO NEUTRAL EAERTH IS REQUIRED IN TNS THIS IS CONFUSING to me kindly expalin me or clarify

thanks

TNS having CT on neutral for earth fault protection is quite normal and does not contradict what I said before. The unique feature of a TNS system is that there is not neutral bars at the LV bus bars nor is it used in plant. In Big power stations or transformers where toroids cannot be applied for earth fualt protection due to cable size or cable configuartion, single earth fualt CT on the neutral is quite standard feature. for the puproses of earth fault protection, yes you will need the neutral ringed with CT but to be used for loading any machine!!

You should however not confuse the two subjects- what we are discussing is "earthing" - AND NOT EARTH FAULT PROTECTION which is a different subject altogether, otherwise you will confusing the non electrical minds a lot.

Put a non-conductive coupling between the pump and distrbution system and then add a ground according to local requirements. If you have no requirements or codes then pick one and document what you did.

What I can understand you are trying to do is to provide protective earth connection to your fire water pump metal parts. there is no problem to ground your fire water pump metal parts to your earthing grid if earthing grid in question is not used also to ground the supply transformer neutral in a standard IEE TT system. this is to say that your neutral earthing in any installation must be electrically seperated from your Protective Earthing grid.

Try see that your transformer neutral earthing and the protective erthing grid are eectrically seprarated as a first. Ground then your fire water pump metal parts, including pump body, electric motor earth terminal, connect it firmly to the general "protectiove earthing grid" and will be safe. Note then that you have only this problem in a TT system. In the TNS system, you dont have this problem and any earthing found in the TNS will then do for personnel earthing protective use because in the TNS, no neutral earthing is required. the installation uses custom made lighting transformers for the LV and single phase load demand.

Rgds,

Percy

There is no need to pull earthwire from transformer to fire pump.

provide earthing to fire pump from existing earth network installed near to pump

You can install grounding electrode at the pump and they will be considered supplemental electrodes as per the code, but still you must provide the EGC that is coming from the transformer and connected to the neutral. If you do not provide the EGC, any ground fault has to return to the neutral thru the transformer which is not allowed by the code.