Criss Cross Method

[Bob Clukey]

I was taught to use the criss cross method when testing fuses while energized. I always verify incoming voltage on the line side first. A-B, B-C, A-C. Then I will place one lead of the meter on phase A line side and the other lead on the load side of either B or C. And then go on the line side of B and the load side of either A or C. I am wondering why this method is safer than placing my voltmeter in parallel with the fuse, i.e. placing the leads on the line and load sides of the fuse?

 

[realolman]

I don't know that it is.

What would make it safer? Safer in what way?

I don't get it.

But then again there's a lot that I don't get.

 

[augie47]

I never knew that was a "safety" thing, but more a "proper" check.
If you only check across the load side of the fuses, a feed thru from a load can give you a false indication that the fuse is good when, in fact, it is not. The criss-cross method avoids this false reading.

 

[LarryFine]

No reason I can see, either. Line-to-line is the highest voltage you can subject your tester to. Across the fuse is the easiest and most telling test to me.

 

[brian john]

Depending on loads whats on whats off, I do it all...........

 

[jim dungar]

Across the fuse is the easiest and most telling test to me.

If the load is off, what reading do you get across an open fuse using your method?

 

[don_resqcapt19]

I never knew that was a "safety" thing, but more a "proper" check.
If you only check across the load side of the fuses, a feed thru from a load can give you a false indication that the fuse is good when, in fact, it is not. The criss-cross method avoids this false reading.

How is checking from the line side of A to the load side of B any different than checking from the load side of A to the load side of B? In both cases a back feed from the load can give you a false reading.

 

[realolman]

I think it would be more important to know what you should be reading, in whatever position you put your leads, before you put them there, and then see if that is in fact what you are reading.

Also to be familiar with your meter and what you might read, such as voltage readings where you might not expect them, with a high impedance digital meter. Or making sure you have it on the correct scale with a Simpson...

I don't know that there are any false readings ... only readings that we mere mortals might misinterpret ...

 

[COFFEE TIME]

i allways check the line side first if the disconnect is hot. a to b - b to c - a to c then i check the fuses using the double X method line (a) to load b - line (b) to load c - line (c) to load b - line (b) to load a - if you don't have the same reading that you had when you checked the line side you have a bad fuse ..an it will be the one that your meter lead is on the load side.

 

[LarryFine]

If the load is off, what reading do you get across an open fuse using your method?

Well, who told you to disconnect the load? D)

Actually, I train my guys to check every combination of the supply first.

 

[jim dungar]

i can't remember any one teaching me a correct or incorrect way to check fuses.

I read about the criss-cross method when I bought my first Wiggy a few decades ago.

 

[iaov]

I know it is probably heresy but I like a Vol-Com "wiggy' for testing fuses like this.

 

[zog]

Make sure your "wiggys" are CAT III rated, many are not.