Fusing for the Control transformer.

[Piratepete]

Hi
Am reviewing a small Control Panel from China.
The Panel operates a hydraulic scissor lift. One contactor DOL 1ph 230V motor. Limit switches, Up and Down buttons.
On the previous model the 230v/24v 50VA control transformer had fuse protection on both sides, 0.3A for the primary and 2 amp on the secondary.

The new panel has cbs, but only one, 1 amp on the primary side. What requirements are there for protecting control transformers? What is good practice these days? Fuses or cbs? It's a long while since I looked at panel design!

Any help please - much appreciated.

Thanks
Pete

 

[johnboy6083]

either or i think, as long as the protective device is suitable for the task. so a CB would have to be a D type IMO. I would also fuse the secondary, but if the cables are rated to takethe max current from that tx then it doesnt need fusing, but i prefer to. It will protect the tx from a short on the secondary side.

 

[malcolmsanford]

I'm old school .........................do like my protection devices for this type of thing to be fuse............ after all you can't repair an MCB with a piece of secreted silver paper from a packet of smokes , like you can for those piddly little glass fuses.

 

[johnboy6083]

i prefer to replace fuses with nails!

then when i get out of prson for killing someone due to incompetence, i use the right gear.

 

[Knobhead]

Protect both sides. Your control wiring is protected then.

 

[Piratepete]

Protect both sides. Your control wiring is protected then.

To protect the transformer you need to protect the secondary side. The main double pole cb is 32 Amps feeding the motor contactor. So if the primary is connected by suitably rated wiring to this CB is that permitted without any sub fusing.? I suppose that the risk is of a fault in the primary that doesn't trip the breaker but could cause a fire. How likely is that scenario?

Cheers

Pete

 

[Guest123]

I use these myself, on both sides depending on loading etc......

Bussman modular fuse carriers and cylindrical fuses

 

[johnboy6083]

The above fuse carriers can be obtained as a direct replacement for MCB's and as such can be used to supply DB's from DBs to afford full discrimination, that can't be achieved by using MCB'S in series.