The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Locked rotor, no burnout
by andey
09/30/16 04:48 AM
Temporarily feeding a panel...
by Potseal
09/29/16 11:05 PM
Massive power outage South Australia
by Meadow
09/29/16 06:46 AM
short circuit??
by Meadow
09/29/16 06:43 AM
Norwegian power?
by Meadow
09/29/16 06:36 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
HotLine1 14
sparky 10
sparky66wv 8
gfretwell 8
Potseal 7
Who's Online
0 registered (), 302 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#205852 - 04/11/12 11:26 AM SCCR and fuses
cgw Offline
Member

Registered: 07/29/04
Posts: 133
Loc: Rochester NY
I have been confused on this issue.
Say you have a 100KA available at the service. Does using fuses at the main disconect (in lieu of a circuit breaker)protect down stream equipment?

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#205856 - 04/11/12 05:43 PM Re: SCCR and fuses [Re: cgw]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6786
Loc: Brick, NJ USA
The fuses in the MOCP provide xxxK at the 'load' side of the fuses. The next equipment downstream would be calculated with that 100K as a starting point. One of the calc methods is 'point-to-point', you may find one version of it at the Cooper Bussmann site.

Watch the ratings of the fuses.
_________________________
John

Top
#205862 - 04/12/12 07:54 AM Re: SCCR and fuses [Re: cgw]
cgw Offline
Member

Registered: 07/29/04
Posts: 133
Loc: Rochester NY
100KA on line side of MOCP. ***KA on load side? 100KA or ***KA as starting point for calculation for the next equipment?

Top
#205865 - 04/12/12 06:03 PM Re: SCCR and fuses [Re: cgw]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6786
Loc: Brick, NJ USA
Let's see if I can sumerize this.
IF you have 100K at the line side, and have 100K fuses, then 100K is the first point. Keep in mind, this is based on a theoretical 100K from the service conductors.

The 'start' point is at the utility transformer terminals; the service conductors, length, & type of conduit are factored in, and the 'line' side terminals are the second point. You basically repeat the previous steps to all your points. IF you have motor loads, there are formulas to include the contributions.

The Bussmann 'Plan Review' Book has the complete scenario; I think you can view it online, & it is available to purchase at a small fee. IMHO, it is well worth the price. It will not make you an EE/PE, but it will provide acceptable data.
_________________________
John

Top
#205867 - 04/12/12 07:35 PM Re: SCCR and fuses [Re: cgw]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6786
Loc: Brick, NJ USA
BTW, there is a fault current spreadsheet you can download over at Mikeholt.com Go to Free stuff and click on it.
_________________________
John

Top
#205895 - 04/20/12 02:38 PM Re: SCCR and fuses [Re: cgw]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
Fuses may not protect down stream equipment, but then again they might.

You can never assume that a protective device, like a fuse, will protect another protective protective device, like a circuit breaker. Fuse-breaker and breaker-breaker combinations require actual testing.

You should never use the 'current limiting' effect of protective devices when performing short circuit calculations for equipment locations.

Let-through currents maybe used when considering the protection of specific non-active equipment (i.e. cables, switches, transformers, and electronics).

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals