Kal vs. PJ, when to fuse?

[kerklein2]

I've just begun wiring up my control panel based mainly on Kal's website and have now started to second guess a lot of things based on seeing PJ's diagrams. Basically, in Kal's design, there's only one fuse, and it protects everything running on 120V and 14AWG wire. Well, almost everything. My question is what really needs to be fused? It seems like Kal's paradigm is to fuse to protect wiring, while PJ's is to protect devices.

With my current plan, the PIDs or pumps could pull up to 7A before blowing a fuse and destroy themselves likely, but at least I didn't start a fire. With PJ's wiring, there's a fuse to protect each pump and PID (and I guess elements too?). Which is more correct? Or rather, which is preferred? I guess that's kind of up to me though right?

Additionally, two gaps I noticed in Kal's wiring are the main power switch and contactor which uses 14AWG but is not fused, and the element lights which also use 14 AWG and are not fused.

Help?!

 

[l3asturd]

There is no easy answer to this unfortunately. Everything is for protection. Normally a device is the cause of a problem so the fuse is used to protect the device from overheating the wiring. Sometimes it seems a fuse is used to protect the device, but it is almost always use to isolate the device from the wiring in the case of device failure.

My personal preference is to protect the wiring itself. I want to protect my relay coil wiring, because relay coils have a history of shorting when failing. I don't really care much about fusing my pump wiring, because I use the 15A circuit breaker inside the panel to protect the pumps in the case of a short. I choose to protect the small gauge wiring powering my PID's , meter, and LED's in case any of them short. To be honest, if a fuse blows, it's because a device has failed. PID's will almost certainly destroy themselves before their intended fuse blows. Solid State devices are way more fickle than a fast acting fuse.

 

[kerklein2]

There is no easy answer to this unfortunately. Everything is for protection. Normally a device is the cause of a problem so the fuse is used to protect the device from overheating the wiring. Sometimes it seems a fuse is used to protect the device, but it is almost always use to isolate the device from the wiring in the case of device failure.

My personal preference is to protect the wiring itself. I want to protect my relay coil wiring, because relay coils have a history of shorting when failing. I don't really care much about fusing my pump wiring, because I use the 15A circuit breaker inside the panel to protect the pumps in the case of a short. I choose to protect the small gauge wiring powering my PID's , meter, and LED's in case any of them short. To be honest, if a fuse blows, it's because a device has failed. PID's will almost certainly destroy themselves before their intended fuse blows. Solid State devices are way more fickle than a fast acting fuse.

This was kind of my thinking. If you are drawing enough current to blow the fuse, the device is probably already toast, so protecting the wiring seems like the way to go.

As for the relay coils, what kind of current do they draw? I picked these up:

http://www.pioneerbreaker.com/ProductDetails.asp?ProductCode=CN-PBC302-120V

They are the same ones as Auber carries, just much cheaper. Wondering what size fuse to go with on those.

 

[l3asturd]

Looks like those contactor coils (2-pole) have about a 167mA inrush current and then normalize at about 38mA. That's assuming the 20VA inrush and 4.5VA specified in the technical specs tab. Also assuming a 120VAC coil voltage. Technically that means you could use a .25A for each coil. If you have 3 coils but never use more than 2 at the same time you could use a .5A fuse to protect them all. Heat will also effect how much they draw, but pretty insignificantly. I chose a 1A fast acting for my coils. I also chose 1A for all my LEDs, PIDs, and meter.

 

[kerklein2]

Doh. Didn't scroll down enough on the tech specs tab to see those specs. Thanks.

 

[bagpiperjosh]

What is the purpose for some people using resistors and fuses together?

 

[lschiavo]

What is the purpose for some people using resistors and fuses together?

That's a good one and found on PJ's diagrams. I cannot imagine a purpose...

The resistors act as a fuse when properly sized and power rated.

 

[lschiavo]

This was kind of my thinking. If you are drawing enough current to blow the fuse, the device is probably already toast, so protecting the wiring seems like the way to go.

I'm with you here. The wiring must be protected. Fusin some things is just overkill.

For example if you didn't have a control panel and were just plugging your pump into the wall, would you worry about fusing it? This would apply to any other cord/plug appliance as well...hair dryer, microwave, blender...they are internally protected.

I actually called Auber a while back and asked about fusing a PID. He told me there is no need as it is also internally protected.

 

[Maxkling]

General Rule of Thumb is to fuse every time wire size is changed. Or if you have a component that can be repaired/rebuilt so there isn't a catastrophic failure on the component. But most of the times there is a spike in amperage the component caused it do it by failing.