USA - emon installation with outdoor primary/sub panels


love the concept of the open source emon system.

my solar pv system consists of 3 arrays with 2 using string inverters and 1 using micros.

the primary load center is outside on a power pole with the power meter. the house and well pump connect to the primary load center. the pv sub panel is in a shed and feeds into another sub panel that in turn feeds to the primary load center. the shed is about 100 feet from the primary load center.

initially i would like to install the system inside the shed to monitor only pv system activity. once this is operating fine i would like to include the primary load center.

it seems that the standard US emon system will work fine to ‘kick this off’. it seems the tx system will be required to incorporate the primary load center, but will the tx system work outdoors?

Welcome, @meyesolarstuff to the OEM forum.

I take it you’ve read the page in ‘Learn’ about using the emonTx system in N.America? The reason I mention it is your split-phase system is slightly different to the single-phase system we have in the UK, that the whole emon ecosystem is designed for. So for example you’ll need two c.t’s and two inputs to measure the house load, because you will not normally have a balanced condition there (the two lines will carry different currents) but if the P.V. and well pump are 240 V only, they’ll only need 1 c.t. each.

How? Presumably, you have another load center or some other sub-panel arrangement inside the house? Will you want to measure individual circuits there, at some point?

Designing for the final setup now is an excellent strategy.

Provided that it has a suitable IP-rated enclosure that’s transparent to 433 MHz UHF radio (or if not, you can add an extension cable to the antenna), and you can get a mains supply both to measure the voltage and to power the emonTx, and there are no solid obstructions in the path, then it should be fine.

From what I’ve read, from the pole you have three cables:

  1. A feed to the house,
  2. A feed to the well pump,
  3. An infeed from the PV.

It sounds as if you’re thinking of putting your emonPi in the shed. Are there any loads there that you wish to monitor (separate from the PV)?
How do you intend making the measurements, with c.t’s or taking digital data from your inverters?

Is there a decent Wi-Fi signal in the shed?

thanks for the reply robert.

i do NOT wish to monitor individual loads like house, well pump, etc.

initially i want to monitor pv power output ONLY. after this is working i wish to monitor power received from poco along with the pv power output. nothing else. not trying to be OCD about this.

primary load center = main panel. and yes, the house has a sub-panel. the power meter, house, shed, and well all connect to the main panel.

i did surmise and confirm that the uk has only 3 wires supplied by poco to home. very surprised. but the extra wire is unneeded with a house wired for 220. and i surmised that 2 of the ct units are required for USA 240vac.

the pv sub-panel, the generator, and a greenhouse sub-panel are connected to the sub-panel in the shed.

so i can connect the emon system to the pv system in the pv sub-panel (output to the shed sub-panel) or in the shed sub-panel (same electrically, different spots).

wi-fi can/will be present in the shed. the mesh signal probably works ok to it now, but is likely weak. i am looking into an outdoor router to connect to the house mesh system for use in the shed. i can monitor from linux (if it supports this) or windoze (least favorite).

might try plug-in extender before buying outdoor router.

wondered if the tx would work in an outdoor enclosure? idk anything about them. yes i can pull 120vac from the main panel to the tx for monitor.

Explain, please. Is that what we call “REC” - Regional Electricity Company?

Fair enough - but a lot of people do want that.

Indeed - most domestic consumers in the UK have one phase at 240 V from a TN-S/TN-C/TN-C-S system - so ignoring the protective earth, two wires only.

That’s indeed correct except where you don’t have a connection to neutral - or where the imbalance is so small that it can be ignored. So if (say) your PV has only the control circuits running at 120 V, then you need only one c.t. and you can double the reading to get the total power.

I think you have in mind the emonPi for that? That’s the main “base” unit that also has the emonCMS software that records and displays the data as a web page, so you…

or Android, whichever you like, it makes no difference. And it’s got Ethernet, so if you have a cable route to the house router, you can have a very solid wired connection into your LAN.

As I wrote, as long as the radio signal can get out, it should be OK, especially as it’s pole-mounted so it should normally have a clear line of sight above people, vehicles etc.

I must remind you to check your wire sizes, because it’s likely that our standard c.t. won’t fit at least some of your cables - the hole is only ½" diameter. There’s a list of suitable c.t’s (some require a minor modification to the hardware) on that ‘Learn’ page.

thanks for the reply robert.

poco = power company

one phase, three wires from what i read. supply, neutral, ground (earth)

"don’t have a connection to neutral’? what does this mean?

the pv array output is 240vac to the pv sub-panel. fronius string inverters and enphase micro-inverters. got a good deal on ebay, so decided to try strings & micros. no long dc runs for me.

the emonpi should work in the pv sub-panel since this is 8 gauge wire. don’t know if UK has wire gauge like the US.

but the tx cts might not since this is service cable 0 gauge. haven’t measured size including insulation w/ micrometer. so are there different sized cts?

back tracking to your comment about monitoring the well pump activity and house load, if another tx was used for each, then these can be included?

really i just want a daily summary of pv power generation and site usage. the total poco supplied and total pv generated appear on the net meter display. but that’s all. no daily or hourly…

You can have that - and a live display updated every 10 s as standard. :smile:

Looking at your supply, I see it as 120 - 0 - 120 V. You can take 120 V from either leg to neutral, or you can take 240 V leg to leg. In the first case, you need a c.t. on each leg because the currents will be different - and the difference flows back in the neutral wire.
In the case of a 240 V load, it doesn’t need a neutral connection, so you only need one c.t. because the same current is flowing in both legs - you just double the voltage or the current or the power to get the right value. The caveat I inserted was, if the electronics of your inverters runs on 120 V but they don’t take an appreciable amount of power (and so don’t appreciably unbalance the two currents in the two legs), you can ignore the error and economise by having only one c.t.

No we don’t, we use the cross-sectional area - my main incoming cable is 25 mm² copper, which our standard c.t. with a 13 mm hole just fits over.

Indeed there are - look here: Learn→Electricity Monitoring→AC Power Theory→Use in North America→Use in North America

Yes - or possibly even just one more emonTx - if there’s room in your pole-mounted box. Although the emonTx has one input that’s super-sensitive, that can be changed fairly easily if you’re happy soldering on a printed circuit board - and then you’d have 4 inputs, 2 for the 2 legs of the house supply, and two (if you need two, you might not based on what I wrote above) for the pump.

robert, thanks for the reply.

a 10s updated display is fine.

of course 240vac US is 120 twice with neutral. in the case of the 3 pv arrays, this is unbalanced on the panel, but there isn’t a huge current presented to the panel. the ct can be connected at the panel feed (output) to the sub-panel breaker for the pv sub-panel.

it looks like the ACT-0750-100 by CCS is the one for this based on the imax & aperture size. would not want solid core, especially for service connect, which is about the diameter of the pinky finger.

as for soldering on a pc board, it depends on the hole/wire size. ye old eyes aren’t what they used to be. idk if there is a working pc soldering iron here, although this can be remedied. if i can see it, i can do it. might have to get 2 tx (just in case).

an auxiliary box from the main panel would be required. i can run a 120v circuit from panel to the auxiliary box for the transformer & the tx. just have to find the right box. plastic would be ok, right? bugs get in these panel boxes. this is rural living and bug abound. wasps, spiders, crickets, etc. is it ok for both tx transformers to be plugged into the same circuit?

The YHDC CTs should fit your Service Entrance Wires if they are indeed 1/0 AWG.
OD for that wire is ~12mm. The wire window in those particular CTs is 13mm.

The ACT-0750 series of CTs are of the voltage output type. (333 mV)
Ideally, you want a CT with a current output, which the YHDC CTs sold in the Shop, are.

thanks bill. 12mm sounds about the size of the pinky finger.

if using this yhdc ct, is a resistor included to avoid open-circuiting the ct?

The burden resistors are on the PC board in the emonTX./emonPi.
(if the CT had a burden resistor, its output would be a voltage vice current)
IIRC, YHDC uses a TVS diode as overvoltage protection.

That said, one should never rely on the built-in protection diode. Rather, treat them as they were
unprotected. i.e connect their leads before clipping the CT on a live current-carrying conductor
when installing one, and detaching the CT from said live wire before disconnecting its leads.

bill thanks for the response.

will diode protect from open circuit condition?

i am a ‘fan’ of doing electrical work ‘cold’ rather than ‘hot’. i switch the breakers OFF before doing electrical work.

Short answer, yes.


Bear in mind even with the main breaker off, the SEWs and bus bars are still hot.
(unless whatever is feeding the load center has been disconnected)


Service Entrance Wires

i have a split system: primary load center w/ breakers for house & shed sub-panels. the pv system connects to the shed sub-panel. so when tripped at the primary load center, there is zilch, nada, nunc, 0 vac to deal with.

We appreciate that, but the main service entrance wires from wherever your power comes from (the final transformer on its pole on the roadside?) and all conductors up to the main breaker, are live. It’s only the downstream side of the main breaker that’s isolated. That’s what Bill is warning you about, because it’s on those S.E.W’s where I think you will need the c.t’s to measure the nett grid power flow (“power received from poco”) - unless of course you obtain that in emonCMS by monitoring and adding all the outgoing powers and subtracting the P.V.

Here’s the emonTx PCB. The socket for CT4 is bottom left (labelled) and the holes where you solder in the resistor are immediately behind it. To give you an idea of the size, the plastic moulding of the socket is a faction under ½" wide. An ordinary 27 Ω 0.33 W metal film resistor fits nicely, and will convert that input to be the same as the others. If you don’t use a 50 mA c.t., then depending on which you choose, you need to either add a resistor there on the other inputs as well, or remove the resistor you can see between the holes and then substitute a different value wire-ended one, or nothing if you choose a 1 V output type c.t.

Plastic will be ok - unless you have rodents that could chew it, and with the right IP rating and the correct glands for cable entry, should be insect-proof.

If you use our a.c. adapter and the 433 MHz ISM band radio, you’ll only need that per emonTx for both power and voltage measurement. So maybe not “both”? But I’d still install a spare socket, because if you needed to add the Wi-Fi ESP8266 for example, you’d need a second socket for a second power supply.

an electrician will do this work. he/she will remove the meter and put the cts over these wires.

what about using the pulse sensor here in the USA? will this work with the tx instead of the cts?

if the resistor fits in the slot, i should be able to solder with a pc board soldering iron. last one burned out. need to get a better one anyway. thanks.

Probably not - because you’ll either not get an indication at all when exporting, or you’ll get a false indication, depending on how the meter itself works. Most UK meters show a solid “On” LED when exporting, but if it does flash when exporting, neither the optical sensor nor you and I can tell the whether it’s import or export - hence the exported energy will add rather than subtract.

Something like this should be fine:

But beware of not having it hot enough - if it’s on the cool side, you stand to do more damage than if it’s hot because the heat will be applied for a long time to melt the solder, and that’s likely to damage the board. You need it hot enough to complete the joint in a second or less.