circuit breaker choice
3

Question

circuit breaker choice

floof (Electrical)

(OP)

18 May 15 08:47

Hello everyone,
I wanna protect a 24V DC - 1A installation (the load is a relay). Can anyone please help me in choosing the suitable Circuit breaker ? And can I use a 250VDC CB in this case ?
Thank you.

ScottyUK (Electrical) · Answer 1 · 2015-05-18 17:03:18

What is the source of the 24V? A couple of little automotive batteries require a different solution to a large industrial system.

Why don't you want to use a fuse? Easier and cheaper for DC.

floof (Electrical) · Answer 2 · 2015-05-19 07:27:57

Well, The 24VDC source is a digital output controlled by a PLC. This outputs are connected to a relay to activate scientific machines in labs. I can't use fuses because all the system is implemented on a rail.

BrianG (Military) · Answer 3 · 2015-05-19 10:33:53

By the system being 'rail mounted' do you mean the standard DIN rail or similar? If so, what about a regular DIN rail mounted fuseholder?

OperaHouse (Electrical) · Answer 4 · 2015-05-19 10:35:52

What are you trying to protect against? One option is a PTC fuse. This is solid state and resets. A nice option when installers are likely to make mistakes. These heat up and greatly change in resistance, a small current always flows to keep the device hot. All power must be removed for a minute or two for them to reset.

floof (Electrical) · Answer 5 · 2015-05-19 11:50:42

@BrianG
Yes the system is DIN rail mounted. we have agreed on installing a circuit breaker. I have found one: Schneider CC60-DC 1A but 250VDC. I didn't find a 24V circuit breaker.
thank you :)

ScottyUK (Electrical) · Answer 6 · 2015-05-19 19:19:00

in the event of a short circuit you will probably find that the source of the 24V DC will shut down to protect itself long before the breaker ever thinks about tripping. That makes the breaker somewhat pointless. The breaker you propose (or the C60H-DC which is what I think you meant) is adequately rated for the duty but I don't know where the excess of current is going to come from.

floof (Electrical) · Answer 7 · 2015-05-20 07:44:18

What if a short circuit occurs in the line between the relay and the 24VDC digital outputs?

mcgyvr (Mechanical) · Answer 8 · 2015-05-20 12:13:46

With breakers/fuses the 250VDC rating is "UP TO 250VDC". Its fine as long as the DC voltage rating is in excess of your operating voltage.
http://www.automationdirect.com/adc/Shopping/Catal...

ScottyUK (Electrical) · Answer 9 · 2015-05-20 17:00:25

If your 24V DC comes from a switchmode power supply the chances are it will shut down faster than the breaker will trip if a short occurs. I said that two posts ago. pc2

itsmoked (Electrical) · Answer 10 · 2015-05-20 20:23:38

Excellent point Scotty.

Keith Cress
kcress - http://www.flaminsystems.com

floof (Electrical) · Answer 11 · 2015-05-26 08:38:38

What if the supply will not shut down? I am pretty sure that these outputs are not protected.
thank you

ScottyUK (Electrical) · Answer 12 · 2015-05-30 20:14:01

Post details of the supply. Saves us guessing.

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