I don’t really understand your problem. This c.t. has flying leads, you need to get those into a 3.5 mm plug (which could be very tight), or you need a junction box to change the wire size, which is where you’d mount the parallel second burden.
The problem is, there’s a very limited choice of c.t’s that have the equivalent output to the “standard” YHDC SCT-013-000. Or put the other way round, the emonTx is designed for that one c.t. and so has a very particular input requirement and no easy way to get around that.
If you want zero hardware change, the only choice I know of is the 400 A version of the SCT0023R, and then you’re working it over only a little more than half it’s rated current - the effect of that will be to almost double the current below the accuracy falls away. You know your application, all I know is what you’ve written. If that won’t be a problem to you, then the SCT023R - 400 A version would be my recommendation.
Hi @Robert.Wall i don’t have experience of mounting burden resistors or connecting flying leads. I also want to reduce the risk of installing something that could be dangerous, which is why i would prefer an ‘off the shelf solution’ if it is available. If its not, and so far you and i haven’t found anything, then i may have to go down that route.
I presume you are aware that a c.t. is a current source, and know what happens if it doesn’t have a burden? That’s why I think the 200 A one worked up to 250 A and with a small external burden permanently connected to the c.t. (rather than via a plug and socket connection) will be safer than the 400 A c.t., because unlike the smaller SCT-013-000, the SCT023R does not have the voltage suppressor to hold the voltage down in the absence of a burden.
Is this for work, rather than a domestic installation? Whilst we prefer the information is shared, if there’s anything that I should know that will make it easier to advise you, but which mustn’t (for whatever reason) be made public here, feel free to PM me.
I don’t think its anything that cannot be shared. I’m happy for other people to learn from me, if I’m getting support from this group in the first place.
My knowledge of electrical systems is limited, although increasing significantly off the back of this forum and developing the meters that i have installed to date.
Would you be happy to provide some more information on how to connect the resistor to the junction box and then to the c.t. I will do some research for the components and how to connect them up in the meantime anyway.
As I wrote, a c.t. is a current source. That means it will attempt to generate whatever voltage is necessary to drive the current into its load, or burden as it’s called. If it is open-circuit, the voltage can rise to the point where the insulation breaks down and the c.t. is destroyed. Conversely, a c.t. can always be short-circuited and this is in fact when it is under minimum load. Many c.t’s have provision for a shorting link on the c.t., which allows the instrument to be safely disconnected. Small c.t’s, such as the SCT-013-000 have two zener diodes or equivalent to clamp the voltage at a safe value but above the normal voltage developed across the burden. “Voltage Output” c.t’s have their burden inside the casing, and must be connected to an instrument that has a negligible loading effect on the output. (This why the SCT-013-030 for example is unsuitable for use with the emonTx/emonPi.) The SCT023R has nothing to protect it, so ideally should not be connected by a plug and socket. When I was in industry, we always insisted on hook crimps and spring loaded terminals for c.t. and tacho connections, so that the possibility of the connection being broken was minimal.
