Protection and earthing of 24v ac circuit to energise solenoid valves

[Deuce]

Sorry here is the link I meant to post. These are available type c and from 2-16a.

https://uk.rs-online.com/web/p/mcbs/7913290/

So all I have to do is calculate the maximum in-rush to choose the suitable MCB each time.

 

[Darkwood]

You gave a link that shows a 100w TX 400/230 - 24ac

If you look at the product image it does tell you that the output fuse will need to be 4amp gG, this may blow with multiple solenoids so a 4amp gM may be wiser, if this still has issues then you need to consider a larger TX, if you fuse the secondary side correctly then the primary can be fused as short circuit protection only and you can uprate it to suit the inrush requirements, I would strap down your secondary on one half and fuse the other side as suggested on the TX - ohms law gives us that rating fuse of 4amps.

 

[DaveHsussex]

Well this is where I am with my thinking too. There is no way of anyone accessing the valves/connection points themselves, so it's basically just metalwork the system is attached to that could transfer current to within reach or a person. And that metalwork is earthed to ground in anycase. Fault finding is also straight forward there is a twist lock connector every 8m cable of the ring circuit so it can just be broken into smaller parts and tested that way. Would only take minutes.

I am indeed most worried about circuit protection. What would you use on the 24v circuit? It needs to be something that won't trip/blow due to the inrush current when the solenoids are first energised (could be 20 at once). The number of valves and therefore the load varies though. But obviously won't exceed the capacity of the cables.

Is there an MCB that would be suitable for 24vac use? We have only used fuses previously (the power supplies were fused). These 24vac are not. Would prefer MCB to fuse as it's faster and instant reset.

Can't you just fuse each valve? I know it's more work, but it would scale with capacity that way. If you had a dead short in a single valve, it would blow the fuse locally at the valve, rendering it dead, but keeping everything else alive and working for your FX.

If there is a dead short in the cables, well...you gotta ask yourself what over current can your transformer take on the secondary side before it dies, is that 4amp on the label? You would have to fuse low anyway to protect it, and fuse the solenoids even lower to at like 1amp so a failure can't pop the main fuse...

 

[PEG]

Hi bud,just three questions...

What is the holding current or rating on those valves?

Can you not use a pilot operated valve,to reduce current?

When is Waterworld II being released?

 

[Lucien Nunes]

Agreed, the transformer is what needs protecting here, not the cable. The 100VA tranny with its 4A maximum output would be toast before any damage was done even to one leg of 2.5mm² let alone a ring. The valve wiring and coils are a different matter, maybe there is value in putting small fuses in the tap-off points.

Ideally you should fuse to fully protect the transformer against continuous overload (i.e. it should eventually trip before the winding exceeds a safe temp) but as it has high thermal mass the protection can be relatively slow. A thermal CBE (Circuit Breaker for Equipment) might suit - you don't need magnetic protection as the short-circuit current is small compared to a mains circuit and might not even be high enough to reliably trigger a magnetic trip if the fault is at the end of a very long run. Not having the instant magnetic reponse will help avoid nuisance tripping on inrush.

Have a look at something like http://www.e-t-a.co.uk/fileadmin/us...rungsautomaten/Thermisch/2_eng/D_1658_ENG.pdf

 

[Deuce]

Can't you just fuse each valve? I know it's more work, but it would scale with capacity that way. If you had a dead short in a single valve, it would blow the fuse locally at the valve, rendering it dead, but keeping everything else alive and working for your FX.

If there is a dead short in the cables, well...you gotta ask yourself what over current can your transformer take on the secondary side before it dies, is that 4amp on the label? You would have to fuse low anyway to protect it, and fuse the solenoids even lower to at like 1amp so a failure can't pop the main fuse...

Thanks,

The issue then is if a fuse blows, it's 8m up in the air above a giant pool of water. So best to keep protection at source of the circuit.

 

[Deuce]

Hi bud,just three questions...

What is the holding current or rating on those valves?

Can you not use a pilot operated valve,to reduce current?

When is Waterworld II being released?

17va holding. And there will be 9 on the circuit. The problem with pilot op valves is that they are prone to failing to close of even a tiny bit of debris finds it's way through. The solution is to use a direct acting valve, as we do. But yes, direct acting valves do have up to 10x the current draw.

As for waterworld 2... I think it took so long to break even the first time it's one film there may not be a sequel of But it's an excellent example of how expensive doing anything with water is. Many films and TV shows end up cutting intended features when they see the cost of making water tanks/fx safe. Although it's also true that sometimes 100k will get spent on something that never actually makes the final edit.. I love my job - sometimes.