ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
EMC Glands on Motors
by Trumpy - 12/01/22 06:12 AM
Ground Rods: Installation and Hook-Up
by Trumpy - 12/01/22 05:54 AM
Happy Thanksgiving all!
by gfretwell - 11/30/22 05:55 PM
Colt Firearms Switchbox
by NORCAL - 11/29/22 01:04 AM
Perfect work light?
by gfretwell - 11/22/22 12:48 AM
New in the Gallery:
240/208 to a house
240/208 to a house
by wa2ise, October 9
Now you know.
Now you know.
by Tom_Horne, September 7
Who's Online Now
1 members (Scott35), 59 guests, and 15 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#205852 04/11/12 01:26 PM
Joined: Jul 2004
Posts: 136
C
cgw Offline OP
Member
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?

cgw #205856 04/11/12 07:43 PM
Joined: Apr 2002
Posts: 7,323
Likes: 7
Member
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
cgw #205862 04/12/12 09:54 AM
Joined: Jul 2004
Posts: 136
C
cgw Offline OP
Member
100KA on line side of MOCP. ***KA on load side? 100KA or ***KA as starting point for calculation for the next equipment?

cgw #205865 04/12/12 08:03 PM
Joined: Apr 2002
Posts: 7,323
Likes: 7
Member
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
cgw #205867 04/12/12 09:35 PM
Joined: Apr 2002
Posts: 7,323
Likes: 7
Member
BTW, there is a fault current spreadsheet you can download over at Mikeholt.com Go to Free stuff and click on it.


John
cgw #205895 04/20/12 04:38 PM
Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
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).


Link Copied to Clipboard
Featured:

Tools for Electricians
Tools for Electricians
 

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
 
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
CharlieE
CharlieE
Indianapolis
Posts: 201
Joined: April 2004
Top Posters(30 Days)
Trumpy 9
NORCAL 5
Popular Topics(Views)
300,508 Are you busy
230,151 Re: Forum
214,962 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5