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#134944 - 12/09/02 02:36 AM wiring rules- installation design o.k.??
amandaamisha Offline
Member

Registered: 12/09/02
Posts: 16
Loc: safat,kuwait,kuwait
Dear Friends,
I in my capacity as a maintenance Engineer, recently took up a Commercial installation where the local supply co. electrical power is sourced through a CUTOUT which has apart from the standard energymeter and HRC Fuses a TP MCCB also.Now downstream the CUTOUT we have a Main Switchboard comprising again an incomer TP MCCB and outgoing TP and SP MCCBs.Now these outgoing MCCBs feed to individual loads like HVAC chiller, Lighting and Power Distribution boards etc.

Now TP MCCB at CUTOUT and at the Main Switchboard has inbuilt thermal and magnetic releases but no earth fault release.Earth leakage protection is provided only at the load end ie, at the Distribution boards,starter of HVAC Compressor, Switch fuse unit of three phase burner etc - what I mean to say no earth leakage protection at main feed.

Is it o.k. to retain the same design or should I opt for a earth leakage release at either the CUTOUT TP MCCB or the TP MCCB at the Main Switchboard by way of adding a Toroid+ relay+ release combination ??

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#134945 - 12/09/02 04:15 AM Re: wiring rules- installation design o.k.??
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
If I'm understanding you, you are wondering if Ground-Fault protection is required for protection of the equipment. This is determined by the rating of the service.
If you are interested in the NEC requirements, see article 230.95.

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#134946 - 12/09/02 04:38 AM Re: wiring rules- installation design o.k.??
amandaamisha Offline
Member

Registered: 12/09/02
Posts: 16
Loc: safat,kuwait,kuwait
Dear REDSY,
You figured it right,I am puzzled if I should add a ground fault interruptor at the main incomer.
Could someone help me out with NEC Code 230.95(courtsey - Redsy) or some other links.

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#134947 - 12/09/02 04:42 AM Re: wiring rules- installation design o.k.??
amandaamisha Offline
Member

Registered: 12/09/02
Posts: 16
Loc: safat,kuwait,kuwait
Dear Redsy,
The rating of the installation is
Voltage - 415 volts, 3 phase
current - 275 amps (MCCB setting)
fault level - 16 KA.

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#134948 - 12/09/02 06:09 AM Re: wiring rules- installation design o.k.??
n1ist Offline
Member

Registered: 02/13/02
Posts: 176
Loc: Malden MA
From her profile, it looks like she is in Kuwait. NEC doesn't apply...

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#134949 - 12/09/02 04:10 PM Re: wiring rules- installation design o.k.??
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Hi Amanda,
Are you indeed in Kuwait? I have no idea what code would apply there, but I doubt it would be the American NEC.

The service sounds as though it is a British-type 240/415V 3-phase wye, and I'm led to believe that much of the wiring in Kuwait is based on British standards (although I'm not certain).

What type of earth connection is provided for this service? Is it TT, TN-S, or TN-C-S?

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#134950 - 12/09/02 10:25 PM Re: wiring rules- installation design o.k.??
amandaamisha Offline
Member

Registered: 12/09/02
Posts: 16
Loc: safat,kuwait,kuwait
Dear Pauluk,
It is indeed a TT installation.We do have MEW regulations here which is purely based on British standards,Kuwait being an erstwhile British colony.Eagerly awaiting replies.

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#134951 - 12/10/02 11:27 AM Re: wiring rules- installation design o.k.??
j a harrison Offline
Member

Registered: 05/22/02
Posts: 112
Loc: southampton, england
Amandaamisha.

if you are in kuwait and the installlation is is similar to the british wiring TT then the installation at origin should have an earth rod to take the fault current down to ground,

the MCCBs and RCDs should protect the appliances and cabling from over load/voltage

the standard way we wire our service from cutouts (service incomer from local PoCo)
the cutout feeds the distribution board via the electric companies meter,

within the cutout would be a fuse, or fuses dependent on whether it is single or three phase, a neutral connection and or a PME (protective multile earthing connection)
As you say yours is a TT system it should have an earth rod, (this should be connected directly to your distribution board together with all the main earth bonding connections.

if you need any other advice please feel free to post them her and we will try to help as there are electricians from all over the world here, and here to help.

John H

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#134952 - 12/10/02 12:29 PM Re: wiring rules- installation design o.k.??
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
If this is a TT installation, then it should indeed include earth-leakage protection (a GFI/RCD) at the main distribution panel.

Without such protection, even a dead short phase-to-earth on one of the sub-feeders would not result in enough current to trip a 275A main MCCB.

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#134953 - 12/10/02 08:57 PM Re: wiring rules- installation design o.k.??
amandaamisha Offline
Member

Registered: 12/09/02
Posts: 16
Loc: safat,kuwait,kuwait
Dear Friends,
As Harrison has stated, we do have an earth rod at the start of the installation and the cutout design is same like he had mentioned.
But the problem is the MCB+RCCB combination protection being just before the appliance or Distribution Board,in case of a earth leakage in the feeder cable(normally doesn't happen ,but poor installation practices may cause it to happen) from the main switch board to the Distribution board or appliance - the downstream RCCB will not sense the fault and the fault will slowly over a period of time develop into phase to phase short and if the magnitude of the fault current crosses the set limits ,the MCCB will trip ,but by then considerable damage to the installation might have occured.

My doubt/ question is there any stipulation that one should mandatorily provide and earth leakage protection at the start of installation of specification as stated in my orginal post ??

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