How to size a fuse. Should I fuse an Output?

[Greg Dake]

Really?

If I'm feeling panicky that my o/p cards may fail, I use some nice weidmuller/klippon interface relays - same width as a regular terminal and come with a nice led! Bet they cost a similar amount to fuse carriers and fuses!

They are good for 5A, so just use 1 fuse and don't fuse the card outputs.

Since when is welded relay contacts a replacement for using a fuse? I use a relay in CONJUNCTION with a fuse...

Greg

 

[Ned_Flanders]

Since when is welded relay contacts a replacement for using a fuse? I use a relay in CONJUNCTION with a fuse...

Greg

They are good for 5A, so just use 1 fuse .

Surely that is what I'm saying?

Going back to the original question though, I think you should look at what the outputs are driving. If is led indicators on a mimic - the likely hood of a horrible short is very small. If you are switching big contactors, especially 24v think again!

 

[Greg Dake]

Makes sense
Greg

 

[Derek]

I have spent time with Marquip, Ward and Red Bud Industries machines from America and I must say, opening a large double cabinet door to a sea of fuses was a new experience. (And fuses in J-boxes and also on the 0V ARGHHHH!!)

Wish Marquip and Ward had put in fuses on their stuff
I work on (or even left some room for DIN fuse blocks).

 

[Roy Matson]

Hi Greg Dake,
You had me worried for a second so I grabbed a Wiedmuller WS1 6/2 and tested it. At 24 VDC with the fuse blown the current reads 5.65 mA (10%), granted that's a lot less than I indicated earlier but if the lamp was incandescent instead of LED it could easily read much higher.
I have only seen it a couple of times where a tank was overflowing because the mA signal was limited to about 16 mA, but that's enough for me. As I said I prefer breakers. I particuarly like the AB ones with two buttons, you can easily see when they are tripped.
I suggest you try it with one of your loops, I would be interested to hear.
Note: Not all loops will top out at the same mA because some transmitters drop more voltage.
Regards
Roy

 

[Roy Matson]

Derek,
What's really annoying, you go to commission a new panel and blow a few fuses - hello, no spares. Even if you specify spares on the drawings you are lucky if the panel shop includes them.
Roy

 

[HJTRBO]

Wish Marquip and Ward had put in fuses on their stuff
I work on (or even left some room for DIN fuse blocks).

I found the Ward flexo and Marquip Downstacker not to bad, it was the Red Bud coiled steel lines I was more reffering to, DAMN!!!!!!

Hey last time I checked in at the old plant the Mitsubishi 58-C knife was still working! I suspect some of you will know how old that dinosaur is!

 

[Derek]

Derek,
What's really annoying, you go to commission a new panel and blow a few fuses - hello, no spares. Even if you specify spares on the drawings you are lucky if the panel shop includes them.
Roy

Whats a "new" panel? Been a long time since I have seen anything
that was not pulled out of scrap yard somewhere or should be in one.

 

[Derek]

I found the Ward flexo and Marquip Downstacker

I know a thing or two about these items.
Small world?

 

[HJTRBO]

I know a thing or two about these items.
Small world?

Absoloutely! I traded our old heaps of machines for a cushy number on new martins and a brand spanker BHS corrugator. Kinda missing the old stuff now, theres not to much a bit basher can do with an integrated embedded systems.

 

[Roy Matson]

xx

 

[theDave2]

What about fuses on all inputs?

A customer had me do that once. They wanted them between the actual input and the field device to "protect the input card". Things went downhill from there.

 

[HJTRBO]

ha ha, let me guess they also wanted a fuse on the earth wire to make sure it didn't melt LOL!

 

[tomwhite007_2008]

Let say money was no object. Should I fuse all inputs and outputs. Solinoid on the valve is 24V 0.25A. What size fuse/ circuit Breaker?

 

[milldrone]

Let say money was no object.

Ahh!!!! But money is the object.

That is why if you fuse every output point of the card, you will save money and time in the long run by being able to fuse the points at a low enough current level to truly protect the card from failure.

Paul

Should I fuse all inputs and outputs. Solinoid on the valve is 24V 0.25A. What size fuse/ circuit Breaker?

I have put on my flame suit allready.

Just fuse the outputs individually, at the value the individual output point is rated for. The object is to protect your output card.

For inputs I fuse the supply voltage in groups that make sense. Like all of the 24V pushbuttons in a operator station would be on one fuse. Or all of the 24V inputs in the north east quadrant of the machine. If you are using a switchmode power supply and you do use fuses on the power supply output, make sure they are small enough to blow instead of just pulling down the power supply.

Where I now work I was able to standardize on small fuses. All of my 1/4 X 1 1/4 fuses are .5 amp and all my 5mm X 20mm fuses are 5 amp.