I have a question about overload protection for I/O modules 120v and 24v. I was curious to see is there any reason to protect a input considering it typically has no load on it. Would you protect a 4-20 ma circuit? What brought this up is I was wanting to protect a set of rNO relay contacts going to a 1756-IA161 input card. I couldn't find much on max current for the I/O but it look liked it was rated for 15ma max current with a load. Which is .015 amps. Is there any material to give me a base idea on protecting I/O modules? Thanks
PLC input and output protection/overloads
- Thread starter mavrick
- Start date
Vlad Romanov
Member
I always add a fuse on digital IO, but nothing on analog for my panels. Some modules have integrated protection, so it may not be needed.
jaden
Member
Assuming 15 ma per input, then a 16 input card would draw approx. 1/4 amp total. A fuse such as 1 amp should work fine. The protection for inputs is more to protect the field wiring and devices than the inputs themselves. For easier troubleshooting, I use 1 fuse for each input card.
Output overcurrent protection will vary depending on output types and loads. Some designers put a small fuse in each output for closer protection levels.
Output overcurrent protection will vary depending on output types and loads. Some designers put a small fuse in each output for closer protection levels.
Mickey
Lifetime Supporting Member
+1. I also do the same for each analog for the same reason above. I don't want
any one device to take down the whole system.
g.mccormick
Lifetime Supporting Member
I do different things seemingly system to system, but one good option that I have done several times is like jaden fused/breaker the 24V+ seperate for each input/output module.
The downside other than fuse/breaker is that the 24V+ is now different wire number module to module. My main reason for doing this is not to necessarily protect the field wiring or input/output module, but instead to keep power up to most of the system if one section fails. So instead of 1 DI brining down power to all IO, it will hopefully at most only effect 16DI channels, etc.
The downside other than fuse/breaker is that the 24V+ is now different wire number module to module. My main reason for doing this is not to necessarily protect the field wiring or input/output module, but instead to keep power up to most of the system if one section fails. So instead of 1 DI brining down power to all IO, it will hopefully at most only effect 16DI channels, etc.
mylespetro
Member
I normally have one fuse per analog input card, but the plant I'm working in now has a 1/4A fuse on every single analog input. Definitely overkill in my opinion, but it's definitely nice to be able to remove power to a specific instrument without affecting the rest by popping the fuse holder open.
g.mccormick
Lifetime Supporting Member
I have worked on systems like that. Very handy with the power isolation per device. It is a bit confusing having the 24V+ be different wired number per device.
James Mcquade
Member
my last jobsite used 250ma fuses for each input and 1 amp output fuses.
james
james
Load * 1.25 is usually standard.
Hence, 16 * 1.25 = 20.
If you had a .8A load, * 1.25 would be 1A
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