fusing a control panel

[bucks7756 0]

I am designing a panel that will be powered by 120VAC. i also have several 24VDC power sources in the panel. Power coming into the panel will go through a voltage conditioner because we have a problem with voltage spikes in the plant. Is it necessary to fuse each DC power source individually and fuse the line coming out of the voltage conditioner or would a 30A fusible disconnect work alright instead of fusing everything indivdually? Most components in the panel are sensors, relays, a plc, safety relays, vision system. There are no motors or other very inductive loads.

[TimWilborne 108]

Your are better and probably required depending on where you are to use branch circuit protection. But aside from the law, if you have a short circuit in your system individually fusing components will make it much easier to find the problem

[bucks7756 0]

That's what I was leaning towards anyway. What is the best way to correctly size fuses? For non motor loads is 125% of continuous load plus 100% of noncontinuous load acceptable?

[OIDMBTRTECH 0]

You need fusing for each circuit and a master fuse to protect the 120 source. You don't want a 30 amp fuse protecting a 2 amp device. The total load fusing exceeding the master fuse size is some what normal as the individual fuse protects the individual circuit. You want your 120 source to typically be rated for about 2X the expected load. Helps with noise and drooping. It also insures you always have enough power available to add another circuit or two with out overloading. Are you using a Sola transformer/conditioner? I have seen them do some right fine clean up on some really trashy line conditions.

[gravitar 3]

A popular brand of AC line filter is the Islatrol.. I use these myself whenever I've got a PLC powered by 120V mains. You can find out about them here: http://www.control-concepts.com/ Just curious about the "several 24VDC power sources in the panel". How many, and why?

[bucks7756 0]

I have 5 dc power sources. 4 are dedicated to each safety relay and 1 is dedicated to devicenet power.

[rwraley 1]

The best place to start is the N.E.C. article 240 and follow leads to other article ansd section numbers for specific devices, environments and applications