Wiring for quality Vemer din rail ammeter (WARNING probably stupid question) - Page 1
Forum section: electronics / general

author: JeLo
author_rank: Contributor
timestamp: October 08, 2022, 01:53:06 am
content: I've searched for more than an hourm I must admit... This is a quality din rail combination ammeter/voltmeter that I managed to get for a decent value sometime ago (nowadays it's way too expensive...).Anyway, my goal is to use it in a DBT build, along with various switches to select different light bulbs and combinations of them.I understand the "S1" and "S2" probably refer to "secondary" and "P1" and "P2" refer to "primary". This also coincides with the fact that this meter uses it's own digitally configurable transformer inside. But... and this is where I'll probably embarrass myself but screw it...1- What the heck are those black rectangles in the wiring diagram ?2- Am I supposed to make an external shunt joining 5 and 6 ? Or does that's simply there as a warning ? I've measured them and they are already physically connected internally, so why the does the wiring diagram has a black box joining them ?Normally I've found out that for wiring ammeters using transformers you just pass the line through the transformer "ring" and then use the CT transformer connections... But this is different, probably because the transformers are already there.....I join in attachment the wiring diagram.And this is the link to the device's page with data/docs about it...https://www.vemer.it/en/catalogue/measurement_and_control/measurement_devices/single-phase_multi-function_device/ev2m-2din_ve149100THANKS!

author: JeLo
author_rank: Contributor
timestamp: October 08, 2022, 08:43:05 pm
content: I think I got what the rectangles mean but still have one doubt... The rectangles are, from what I searched regarding symbols, instantaneous polarity markings. Three symbols can be used with the same meaning (to avoid confusion with other similar ones), a point, an "X" or those rectangles (maybe squares, they're mostly rectangles in this...). Only one can be used per transformer winding and only should be placed near the end of the winding...This coincides with the letters p and s on the small drawing on the bottom which, like I said above, probably mean primary and secondary... It wasn't clear because the tranformer windings are not shown...Maybe someone can come up with a better explanation on what it is, but this is what I found that makes more sense so far...Anyway, now I should know how to connect it but I don't, well sort of... I think the connection should be made on terminal 5 for the neutral and 8 for the phase, with the load connected externally between both. From terminal 8 the voltage measurement is made and terminal 5 connects the transformer's primary to the neutral. But in that case what is terminal 6 for ?!I don't want to connect it before being sure...

author: JeLo
author_rank: Contributor
timestamp: October 08, 2022, 09:08:19 pm
content: Another option would be connecting the load's neutral to terminal 6 and then the neutral wire to terminal 5, but wouldn't that make the whole current go through the transformers secondary ?!

author: JeLo
author_rank: Contributor
timestamp: October 12, 2022, 05:36:42 am
content: I found the answer, the datasheet from the link above says the ammeter is to be connected through an external CT x/5 transformer. CT probably meaning current transformer... Now in the user manual it doesn't mention any of that...So my assumption that this had some internal transformer with selectable taps is .. I don't know where I got it, but it's totally wrong. It is however programmable to accept various transformer ratios, but of course a matching transformer has to be in place, otherwise readings will be in the wrong scale/messed up...You're welcomeAnyone has any experience / suggestion for a good external CT x/5 ? Are those cheap chinese ones any good, I guess it doesn't make much sense to use them for a meter like this... I don't know...