Checking a blown fuse.

[Waxman]

Both my SS bays went down today; it was also a fact that my IBA was down; door jumped track.

I checked the fuses but they seemed to have continuity. Luckily my friend Eric said to opo the fuse out and re-check. I did and he was correct; no continuity!

Thanks Eric. I didn't know that the proper way to check a fuses continuity was with the fuse in question out of its holder. Now I know!

 

[mac]

You can read a fuse without removing it from its holder. Just use a volt meter instead of a continuity meter. If you read 0 volts while the system is energized, it's good; if you read a voltage, it's bad. Your way is preferred, unless you run into one that is soldered on a board.

 

[I.B. Washincars]

I would imagine Wax is like me and many other operators and use the M-N-M principal when checking a fuse. I have a cheapy Radio Shack meter with a needle. When I touch each end of the fuse and get "M"aximum "N"eedle "M"ovement, I know it is good. Who needs a fancy shmancy meter with all those silly numbers on it?

 

[bigleo48]

I have come across some type of fuses (like ceramic) that will show continuity out of the hold, but cannot pass higher current level.

The reason that you need to remove the fuse is that you are likely measuring the coil continuity and not the fuse.

Yes a cheap meter will give you a "good" or "bad" reading. But like anything else, better specs (tolerances) come with a higher price.

Big

 

[2Biz]

On an energized circuit, The way I check for a blown fuse is to check for voltage at each end of the fuse to ground. A blown fuse will have voltage on one end and not the other....A good fuse will show voltage to ground at either end.....

If the circuit is not energized, then you need to remove the fuse and check continuity....

 

[RykoPro]

If you are checking fuses on a three phase motor you must remove each fuse to check continuity otherwise you are reading the resistance of the motor windings. To properly check voltage though a fuse you should read from the power source common to the load side of the fuse. With three phase you can read across the legs. Sometimes circuits will show continuity with the meter but not under load. The voltage used to check resistance with a meter is very small as compared to actually putting a working load on the circuit.

 

[2Biz]

Just so I'm not putting false information out there, is the way I check for a blown fuse not correct? Or maybe not the most correct?

 

[RykoPro]

Just so I'm not putting false information out there, is the way I check for a blown fuse not correct? Or maybe not the most correct?

Depends on how your wash is wired and what circuit you are checking. Ground is not always the common to every circuit. For the most part how you are doing it will work but it is not always the case. Always a good idea to have the electrical prints so you know what you are checking.

 

[Ghetto Wash]

Doesn't matter how its wired, if you have voltage across a fuse, its bad - period, end of story.

No voltage, does not tell you anything without further investigation - look at schematic, pull fuse and check continuity, etc.

 

[RykoPro]

He was asking about checking from ground to power, I was just saying ground is not always the common of a circuit.

 

[Ghetto Wash]

He was asking about checking from ground to power, I was just saying ground is not always the common of a circuit.

Agreed.

I wasn't trying to contradict you, just adding my .02 on how I check fuses.

 

[MEP001]

Can't you just touch your tongue to it like you would check a 9V battery?

 

[Eric H]

Can't you just touch your tongue to it like you would check a 9V battery?

I clearly remember my big brother tricking me into doing that. Next time I see him I'm giving him a kick in the pants.

 

[sparkey]

You can read a fuse without removing it from its holder. Just use a volt meter instead of a continuity meter. If you read 0 volts while the system is energized, it's good; if you read a voltage, it's bad. Your way is preferred, unless you run into one that is soldered on a board.

This only works if their is a load on the circuit. If a contactor is open or a wire is off it will read zero if the fuse is good or bad.

 

[sparkey]

On an energized circuit, The way I check for a blown fuse is to check for voltage at each end of the fuse to ground. A blown fuse will have voltage on one end and not the other....A good fuse will show voltage to ground at either end.....

If the circuit is not energized, then you need to remove the fuse and check continuity....

This doesn't always work. Some 3 phase systems are not grounded so measureing to ground will not always work. The best way is to measure across the phases or in the case of a control circuit to the neutral wire. Measureing to ground will also sometimes give you readings if the fuse is good when the fuse is blown and the circuit is backfeeding through a device like a heating element.

 

[2Biz]

Thanks for setting me straight. Guess I was thinking in terms of single phase where the ground and common are most always tied together. I agree, in a 3phase circuit, you'd want to check voltage between load and the common.

The original poster was testing a fuse on door that had jumped track...Most door openers are 110v and 220v....Then we jumped to 3 phase!

 

[RykoPro]

3 phase does not have a common.

 

[2Biz]

I'll shut up now...

 

[RykoPro]

Do not be discouraged by all of us know it alls. If you have questions please ask; better safe than sorry. When I got out of electronics school all I had was the basics. As soon as I graduated, I was hired by Ryko. The on the job training was priceless and soon I forgot most of what I learned in school. I have seen some pretty strange electrical circuits and even stranger supply power from the electric company so nothing surprises me.

 

[Ghetto Wash]

RycoPro, your PM inbox is full. I'd like to PM you. Can you clear me a little space?