EpicWill (Customer) asked a question.
Hi guys, I'm using the ADM100C-LN meters in conjunction with the CTF-5SFT-0050 50:1 CT's. I'm running 7 heaters total, two of which are well under the 5A input limit of the meters and one is just a hair above it. What I've calculated for each is below:
Zone 1-3: 4000W @ 460V = 5.02A
Zone 4: 2x 1.5kW heaters at 240V = 7.21A
Zone 5: 1x 350W @ 240V = 0.84A
Zone 6: 2x 2kW @ 240V = 9.62A
Zone 7: 2x 400W @ 240V = 1.92A
Zones 5 and 7 I don't need a CT on as they're well under the 5A max input of the meters.
Zones 1-3 I believe I do as they're above the 5A limit for the meters but the smallest I can find is 50:5 which would require 9 wraps through the CT to get it down to 5.55A max input.
Zone 4 would need 6 wraps to get down to 8.33A max input.
Zone 6 would require 5 wraps to get down to 10A max input.
Does this all sound correct or is there something I'm missing? Thanks in advance.
The CT you spec'd is 50:5 ratio or 10:1, so your 5A zones 1-3 would deliver 0.5A to the meter with no extra wraps.
Zone 4 with CT would send 0.721A to the display and Zone 6 would send 0.962A
Adding extra wraps would effectively cut the CT ratio in half each time, or add the amount of current in the conductor to what is transformed, so two wraps on all the zones with CTs would get you around 1A on zones 1-3, 1.4A on zone 4 and about 2A on zone 6.
EDIT: I didn't do the math on your watts to amps for each zone but it looks a little off and would recommend you measure it before installing anything. If those are measured current readings, then you may want to calculate peak expected amps based on the heater wattage ratings and actual voltage.
Zone 1-3: 4000W/460V = 8.7A
Zone 4: 2(1500)W/240V = 12.5A
Zone 5: 1(350W)/240V = 1.45A
Zone 6: 2(2000W)/240V = 16.672A
Zone 7: 2(400W)/240V = 3.33A
With these theoretical peak values, I would use CTs all the zones above 5A with no extra wraps. (maybe one extra wrap on zones 1-3).
Ok that seems to be an easier way to look at it. So in that case I could use a single pass through all of them and just adjust the scaling in the meters themselves correct?
I played around with the meter software a bit but there's no manual I can find on how to use the software. There is a tab for CT where you can input the primary and secondary turns of your CT but there's nothing that says what that will do. Can I run a single pass and just put 50 and 5 in and it'll auto-scale it? I don't know, it doesn't tell me what that does. There's also a scaling tab where you can set the scaling but if the CT tab will do that then I don't need the scaling tab. I'm not sure though
Even though zones 5 and 7 are below 5A, you still need a CT. The CT inputs are not meant to take the full voltage I can't imagine. Use CTs, either buy CTs with the correct scaling, or wrap the wire multiple times to get the CT secondary higher.
Are your heater single phase or 3 phase?
I actually emailed AD about not needing the CTs on those two and they said I could hook them up directly, so I don't know about that. The paper that came with the meters also doesn't list an input voltage range either. If I were to do that with those two small ones, I'd need like 61 wraps on one of them to get an almost 5A output from the CT. But then again, these meters have scaling in the software so I could just scale it.
The heaters are single-phase I believe but they're connected line to line rather than line to neutral. Zones 1-3 are 460V and the rest are 240V.
Looks like you're correct. Looking at the MFR page for these meters (Amp Meter vs. CT Meter - Trumeter Knowledge Base (helpscoutdocs.com)) and looking at the AD product page it would seem these are the CT meters so I would need CTs on the other two zones. I'll just have to add wraps and change the scaling in the software I suppose.
The only thing I can't find is max voltage for the meters. The non-CT one says 42AC/DC but the CT one doesn't say. If I do the 460v one through the 50:5 it'll leave me with 0.1A @ 9.2V. If I do 5 wraps to get up to 1A for some resolution that puts me at 46V. Or 4 wraps for 0.4A @ 36.8V
I had not considered the voltage if you were to connect the display directly to the heater leads. I would definitely recommend using CTs on all of them, with multiple wraps on those that would present less than 0.1A at the CT output with a single pass.
I ended up doing just that. The 50:5 were on BO from AD so I used two of the 75:5 that were originally in the cabinet on the two highest amperage circuits and the 50:5 on the rest.
I doesn't seem that the meters auto scale after putting in the CT specs in the software. I hooked a spare 3kw heater to one zone and it should have read 3.76A but was only reading about 2.3A. I'll have to put a current clamp on it to see what it's actually reading and then scale them in software