Heater Circuit Fusing

[plc noob]

We have a new extruder that came in a couple weeks ago and it has a ferraz semiconductor fuse for each of the barrel heater circuits.

This is a global style fuse and fuse holder http://us.ferrazshawmut.com/oem/media/pdf/A70QS%20-14F%20-22F.pdf

My question is from a design standpoint is there any reason a standard fast acting class cc fuse could not be used in this type of application?

 

[David_Emmerich]

No reason except the supplied fuses cost more.....your local CED dist will love you. Why not swap out to AD's C/H din rail cb's? At $23 ea for a 3pole unit they are cheaper than a fuse holder....

David

 

[plc noob]

I would prefer to use breakers everywhere.

What applications should you not use a breaker but use a fuse?

Just trying to gain general knowledge on this subject.

 

[theDave2]

The semiconductor type fuse is there to protect the SCR's (triacs) / power electronics that are part of the heater controller. If you get a heater element short, you want the fuse to blow vs the power electronics. It is a very fast acting fuse. You should see that the fuse is a bit higher amps than you might think, but this is needed.

Do not replace it with other types. Do not replace it with a CB. See the user manual for the heater controller as it will tell you the type and value of over current protection that is acceptable.

 

[David_Emmerich]

Where you need really fast circuit protection you can't beat a fuse...but most of the time, for motors and heaters, a series "D" curve CB will do very nicely. You must watch the "curve", that is the response to current vs time, when you select CB's, and match it to your type of loading. "D" curve CB's will pass high inrush currents like a motor or transformer, but I also use them on heaters...two different part numbers with only a letter difference between them is too much for the old farts in our shop....

David

 

[Plastic]

Semi conductor fuses vs Breakers

The OEM that built your extruder probably is using Solid State Heater Power switching devices. The OEM elected to use semi conductor fusing to protect the solid state power devices. This has been typical methodology for quite some time. I don't necessarily buy into "this is the way we allways have done it" mentality. There is nothing wrong here, but you do have options to consider.

The single replacement semi condustor fuse might actually be MORE expensive than the power switching device. When the fuse blows, you may have a hard time finding it locally, unless you have them in your spare parts supply (and keep that maintained).

NEW Product available now that was not a few years ago. Check out Bussman, the have a DFJ fuse. This is a CLASS J fuse but it is also engineered with a low (I squared T) rating to protect solid state drives and solid state power switching devices. http://www.cooperbussmann.com/pdf/58901238-c17a-42a2-8cc1-3fef6d776864.pdf

We had one customer who wanted no fuses, and wanted Circuit breakers. Keep in mind the breaker may not protect the solid state switching device, but in the solid state switching device is relatively economical, then who cares? Breakers are easy, and readily reset.

ONE CAVEAT about using breakers. There are many SUPLEMENTAL Circut portective devices that are not rated for the purpose. If you elect to use circuit breakers, make sure you specify breakers that are BRANCH CIRCUIT RATED. This is a NFPA 79 7.2.11.3 requirement

 

[theDave2]

Here's a couple of links for the OP to read up on.

Main page of a Watlow heater controller:

http://www.watlow.com/products/controllers/power/dinamite.cfm

Some info on them & fusing:

http://www.watlow.com/literature/prodtechinfo/files/controllers/din a rev h.pdf

http://www.watlow.com/literature/specsheets/files/controllers/winfus0703.pdf

 

[plc noob]

These Fuses are before the ssr so how will they protect the ssr from heater failure/short?

Also what about using an electronic overload? Instead of a fuse or breaker.

Seems like an overload would give the speed of a fuse if set correctly and the convenience of a breaker?

Should they be fused before or after the ssr? Or both?

 

[504bloke]

I use siemens ssr's on extruders with a B type siemens breaker behind them, if sized according to siemens tech literature and the correct ssr is chosen the ssr is 100% protected from heater short circuit and short to ground.

 

[leitmotif]

I think the whole issue of fuse vs breaker comes down to a couple decision points
1. Convenience
2. Cost
3. Personal choice

I like using circuit breakers too. Reliable, dont have to mess with em, dont have to stock a lot of spares. ASSUMING you understand the load and you match the breaker to the load.

Fuses are a pain in the neck. You have to stock a wide variety and put up with the stocking issues including some boob put the wrong fuse in teh drawer - and why am I the only guy (or am I the only guy who actually digs out a magnifying glass to read the numbers?) that seems to get the wrong one every time? Back to the parts bin sigh.
The last guy forgot to say he took the last ones and the list of problems with fuses goes on.
There is the cost of operator error which I think is multiples of the cost of the fuse.

In some cases you are forced to put up with fuses as already stated to get quick interruption to protect valuable equipment. So what that comes down to is what is more expensive the fuses or the equipment.

The last thought - if this is brand new equipment will you void the warranty by changing things around?

Dan Bentler