ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Happy Thanksgiving
by gfretwell - 11/24/20 05:44 PM
What does your work place look like?
by HotLine1 - 11/23/20 03:35 PM
Where is Everyone?
by Lostazhell - 11/21/20 04:17 AM
Ground fault remover :-)
by dsk - 11/21/20 02:47 AM
Work Gloves?
by gfretwell - 11/20/20 10:17 PM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
1 registered members (NJwirenut), 21 guests, and 16 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
fusing primaries #50759 04/11/05 09:58 AM
Joined: Nov 2001
Posts: 45
B
bill woods Offline OP
Member
I just got a call from a friend. He wants to know what size to fuse primaries on a 120v power supply. Secondaries are 12vdc 10amp. Thought I knew but can't find my info books. Anyone??...

Work Gear for Electricians and the Trades
Re: fusing primaries #50760 04/11/05 10:35 AM
Joined: Mar 2002
Posts: 582
R
Ron Offline
Member
First place is manuf info.
If none, then a fair guess is
12V x 10A = 120W output
The input will be at least 120W plus losses in the conversion.
So a start would be 120W/120V=1A fuses


Ron
Re: fusing primaries #50761 04/11/05 12:02 PM
Joined: Jan 2005
Posts: 18
B
BPiersel Offline
Member
If you fuse this at 1A, you are likely to have nuisance blows from the current inrush at startup.

What are you trying to protect with the fuse? If you are trying to protect the power supply from an overload, put the fuse on the output, not the input. It is difficult to determine a fuse size that will blow on an overloaded output without having nuisance blows. Check the specs on the power supply. Some have internal overload and short-circuit protection, so you may not even need to fuse it to protect against overloads.

My suggestion would be to size the fuse based on the wiring supplying the power supply, to protect it in case of a fault internal to the power supply. For 18 AWG, fuse it at 7 A or less. 5 A or even 2 1/2 A would work.

Check the manufacturer's specs first for any fuse size recommendations.

Brian


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
SafetyWired
SafetyWired
Pa, USA
Posts: 44
Joined: July 2013
Show All Member Profiles 
Top Posters(30 Days)
Trumpy 9
Popular Topics(Views)
271,918 Are you busy
205,794 Re: Forum
193,888 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3