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fuse voltage rating?

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cliffforrest

Member
Joined 2004
M Gregg said:
I agree,

However at instant short circuit there is no load to supply..

Regards
M. Gregg
Click to expand...

Well, that is not how I would analyse it.

At the "instant" of short-circuit there is still a supply, zero load resistance and an infinite load current.

Obviously that is all modified in the real world by all the circuit impedances, so referring to the "instant" of s/c doesn't help much. Nothing in engineering happens instantaneously.
 
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WILD1

Member
Joined 2012
"I think this is the point you would have 120V across an open fuse"

You don't have a 120 volts across an open fuse. That is my point. Grab the grounded side or the load side of a blown fuse. No voltage. However grab the supply side in one hand and ground in the other hand. Guess what,you get the hell shocked out of you. You have voltage on the supply side just no current flow with the fuse blown thus no transfer of energy [volts] to the grounded side. Sorry guys I am struggling with this Quote feature kind a new to this.
 
M Gregg

M Gregg

Disabled Account
Joined 2010
WILD1 said:
"I think this is the point you would have 120V across an open fuse"

You don't have a 120 volts across an open fuse. That is my point. Grab the grounded side or the load side of a blown fuse. No voltage. However grab the supply side in one hand and ground in the other hand. Guess what,you get the hell shocked out of you. You have voltage on the supply side just no current flow with the fuse blown thus no transfer of energy [volts] to the grounded side. Sorry guys I am struggling with this Quote feature kind a new to this.
Click to expand...

If you put a multi-meter across an OC fuse set to voltage you will read 120V. Reason is the one side of the meter is on supply the other side is conducting through the load to neutral. The current through your meter is small the volt drop across the load will be small. The fuse is not conducting so one side is at supply the other side of the fuse is connected to the load which should be at neutral. I undstand what you are saying its just that a meter will not read 0 volts across an OC fuse..

Regards
M. Gregg
 
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WILD1

Member
Joined 2012
Yes , because it is reading the difference in voltage from the 2 sides of the fuse. But that doesn't mean that you have voltage on both sides. You have a 120 volts on one side and 0 volts on the other side. The difference is 120 volts so your meter reads 120 volts. I think an article on how a meter really works would help.
 
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sofaspud

sofaspud

Member
Joined 2005
You don't have a 120 volts across an open fuse. That is my point.
Click to expand...
That is incorrect. Any open circuit has the full voltage across the open.
Voltage is electrical potential between two points; in this context supply and ground are simply two possible points. As is one end of the open fuse versus the other end.
I think I understand your Kirchoff-ian explanation, but it's unorthodox and confusing.
 
TheGimp

TheGimp

Member
Joined 2009
Kirchhoff's circuit laws - Wikipedia, the free encyclopedia

From Wikipedia


"The directed sum of the electrical potential differences (voltage) around any closed circuit is zero,"

Now you are trying to define a closed loop to be an open loop.

If you define the circuit element to be infinite, you define the current flow around the loop to be zero.

You can not have an IR drop in a circuit element if no current flows.
 
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