ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Any Woodworkers here?
by gfretwell - 05/11/21 04:29 PM
Lock-down Thread
by gfretwell - 05/11/21 12:30 PM
Do You Travel?
by gfretwell - 05/11/21 12:16 PM
Your favourite food?
by gfretwell - 05/11/21 12:00 PM
Just be aware of this...
by gfretwell - 05/10/21 07:30 PM
New in the Gallery:
2020 - 2021 Winter Project
Garden 2021
Who's Online Now
1 registered members (Scott35), 15 guests, and 16 spiders.
Key: Admin, Global Mod, Mod
Previous Gallery
Next Gallery
Print Thread
Rate Thread
Explain the parallel fuses ?? #213509 05/26/14 05:39 PM
Picture 021.JPG
Joined: Apr 2002
Posts: 7,258
HotLine1 Offline OP
Member
Explain the parallel fuses ??

Explain the parallel fuses please
Tools for Electricians:
1 Comments
Re: Explain the parallel fuses ?? [Re: HotLine1] #213515 05/27/14 12:11 AM
Joined: Jun 2004
Posts: 1,273
T
Tesla Offline
Member
1200A can (barely) be seen next to each bus -- down low.

The 600A frame size fuses are ganged because -- at one time -- that was a popular size limit for 250VAC fuses (blade style)

The operative assumption was that such matched sets would blow in sequence and that they'd always be replaced in pairs -- if not the entire sextet.

IIRC, this disconnect feeds a major retail establishment -- and the power flow is backwards: line is at bottom, load is at top.

It feeds a distribution panel on the other side of the wall... just as ancient. Consequently, these fuses did not have more than a prefunctary purpose. The many smaller fuses just a few feet away would protect the branch conductors and all sub-feeders.

These (MAIN) fuses could then only blow if some anarchist placed a bomb at the distribution board. (!)

You'll note that they did their duty for decades on end.

It was installed generations ago. (30s to 40s?)

The NEC at one time required disconnecting means exterior to any structure.

(In the very beginning the switch was to be thrown OFF when a building became unoccupied.)

This safety switch was probably installed per the Fire Marshall's specifications. Being in an urban setting, the line side power was coming in from below. Rather than fuss and bother, the power flow through the switch was simply reversed.

Obviously, none of it would fly today: exposed bussing, wrong way power flow,... even the fuses are standard blow -- not slow blow. Also note the extremely wide single layer copper bussing. It's simply not done anymore.

Today the Fire Marshall would be satisfied by a shunt trip MAIN for his crews. The entire box would never be necessary.


Last edited by Tesla; 05/27/14 12:18 AM.

Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

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

 

Member Spotlight
RH1
RH1
California
Posts: 22
Joined: August 2009
Show All Member Profiles 
Top Posters(30 Days)
Trumpy 19
Admin 8
Popular Topics(Views)
278,868 Are you busy
212,027 Re: Forum
199,064 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3