As part of energy monitoring service ( free commercial trial) I'm working on I would like to install several CT sensors for use later. While I am familar with electrical services, I plan to use a local electrian to open the boxs and install CT sensors (pub has 3 phase supply four panels - quite complex). Ideally the sensors would be clipped onto cables inside electrical panels, labled and left tied up out-side for use by myself as trail system is built ( leaving me with some time to develop system).
I'm using Yhdc SCT-013-000 current transfomer Transient-voltage Suppressor, with EmonTX, Emonbase, Emoncms and may integrate towards Raspberry Pi ( just arrived but thats another story).
Question is about safety, the Yhdc SCT-013-000 has a Transient-voltage Suppressor so I assume this setup should be ok. However I'm still a be worried about leaving these clipped around cables carrying up to 80Amps (worst case) for weeks.
Looking forward to your comments
Cheers
Peter
Re: Current Transformer
PeterN
Don't do that. I think the 'Transient-voltage Suppressor' isn't that specifically, though it will function as such but it won't protect the emonTx input, I think it's only there to prevent dangerously high voltages if there's no connection to the c.t. The best solution would be to leave the c.t.s loose in the panel to be clipped on later. Failing that, short them but make sure the circuit is dead before you remove the short and plug them in to the emonTx, else you'll get 20 V or so at whatever current the c.t. can muster. It might not do you a lot of damage but if it touched the wrong part of the emonTx first, you could easily have a dead emonTx.
Re: Current Transformer
Hi Robert, thanks for comments, I suspected as much. However I had hoped worst case was that I would have to build a dummy CT plug with burden resistor and then swap over to system emontx as they are needed or not. The issue is basically I will use electrician to access the cables within two bespoke panels and would like to be able to connect quite a few CTs to the cable when electrician is present for use as I see fit during trial. The alternatives is to get an electrian back each time I need to connect new CT or else open panel myself once I become more fimilar with this layout.
I had assumed that it would be normal enough to plug in and out of emontx without unclipping from cable (oops done this serveral times already on home system). Would dummy CT plugs terminated with burden resistors be sufficient and be careful pluging into emontx e.g. emontx in battery enclosure would mean they won't touch off other components.
Cheers
Peter
Re: Current Transformer
There would be no real personal safety issue if you left the c.t's open circuit, but for the fact that one of our forum members has a 30A version, which has a built-in burden, and when he received it the soldering was so ropey that the burden was open-circuit. So to avoid damage to the c.t, or anybody else, I'd simply short them until you are ready to connect. I wouldn't even bother with a dummy burden, c.t's are quite happy working into a solid short circuit (just as 'ordinary' voltage transformers are quite happy working into an open circuit). It's open circuits they don't like (they can either be permanently magnetised if it's an iron core, or they'll flash over).
If you could make sure the circuit was unloaded or only lightly loaded when swapping from the shorting socket to the emonTx, there should be no problem, but you only need 18 A to clip the output at 22 V with the zener diodes.
Make sure all the c.t's face the same way when you're installing them - see the notes in Building Blocks, else you'll have some showing +ve power and some -ve!
Re: Current Transformer
Thanks Robert. That's sound good. I'll build a few short cct. jack sockets. I'm sure I can get access during low usage period to add to emontx.
I've been caught out on that before CTs facing wrong way before, giving negative values and now I lable them with permenant marker. Cheers Peter