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I’m trying to positively identify what is on each of the four terminals in a pool pump’s timer box (before replacing it with a z-wave smart switch):

Timer box with cover open, external view

The trick is that both line- and load-side wires are black, and I’m not sure if this is 240V (if it is, it would be my first foray with AC beyond regular 120V’s hot/neutral/ground).

Terminals 1-4, corresponding to the placard visible in the external view, also showing the 2 white wires to the timer and 4 black out the conduit

This pre-existing setup’s wiring has worked perfectly for the decade we’ve been in the house. Over the weekend, the timer’s switching mechanism failed mechanically.

In addition to identification, what is the surest, most expedient method to verify each wire’s identified function using a multimeter? (I hope that’s not too much to think possible, given the rest of what I described!)

Also, though the focus of the question isn’t on the z-wave timer/switch I’d be replacing this Intermatic with, here are the wiring instructions, assuming everything checks out OK as 240V:

GE smart switch connections for 240VAC

From the instructions, I’m able to note that one wire I can’t identify in the pre-existing installation is a ground. And for what it’s worth, the instructions call for adding a jumper (not included) across 3 and 5 when configured for 240V. I’ll be checking the NEC myself or posting a separate question for what color to make that.

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    Can you carefully use your meter to measure voltage between terminal 1 and terminal 3? (the two terminals labeled "LINE" on the insulating shield, in other words) – ThreePhaseEel Dec 10 '19 at 1:30
  • from my take on the guide termnal 3 is internally connected to terminal 1 so use the same colour as terminal 1. byjasco.com/media/manuals/14285-QSG_V1.pdf – Jasen Dec 10 '19 at 22:42
  • How many HP is the pool pump? – ThreePhaseEel Dec 11 '19 at 0:45
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the terminals are thus:

  1. Phase one line
  2. Phase one switched
  3. Phase two line
  4. Phase two switched

The little white wires run the timer motor

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    Label the wires before you disconnect. – Mattman944 Dec 10 '19 at 9:42
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    yes, also also, check the other end of that conduit. – Jasen Dec 10 '19 at 10:11
  • @Jasen Check which other end for what? My impression was that the two black line wires were running into the electrical panel outside the house and that the two black load wires ran to the pump motor (Hayward, I presume, like the rest of the system, but I wasn’t seeing any readily identifiable markings). – lionel Dec 10 '19 at 17:22
  • @Mattman944 Always a good thing to remember to have on hand before starting – and to do in the moment! I was also thinking to cut back and re-strip the wires that have cracked insulation. I presume cracked by years of chafing against the protective insulating card. – lionel Dec 10 '19 at 17:28
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This is a double pole single throw switch. It is designed to run on straight 240V. If you look at the insulator cover, you'll see that #1 and #3 are the line, feed, terminals. If you hook your multi meter to those two terminals you should get 240V. #2 and #4 are your load wires. They will go to your pump. The two white wire hooked up to #1 and #3 supply 240V to the motor that runs the timer. I have seen people switch the line and load connections and then wonder why the timer doesn't work... that's because the motor would only run when the timer is manually switched on. There should be a ground wire run to the box. Also, you mention that you want to install a smart switch. Those may require a neutral wire depending on the switch so you'd have to run that.

If it's just the timer motor that has failed, you can get a replacement at many home stores. If the switches are the problem, you can get a completely new switch and just switch out the guts and not have to replace the box. Good luck

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    Logically a 240v smart timer /switch should run fine without a neutral. The need for a neutral with a smart switch is same as for motor here. Problem on 120v is 2nd wire in the circuit, neutral, is not switched and therefore not needed with a manual switch and therefore often not present. – manassehkatz-Moving 2 Codidact Dec 10 '19 at 14:30
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    @manassehkatz-ReinstateMonica Good point Mr. Spock. I didn't think about that. Definitely something for the OP to check if installing one. – JACK Dec 10 '19 at 15:37
  • @JACK And since this is a “first forays into 240V” question: I’ve been tendering to myself the assumption that the two line wires are fully interchangeable with each other and likewise the two load wires. If they weren’t, I’d be having to identify which is wire 1 and which is wire 2 on the line and load sides. – lionel Dec 10 '19 at 18:32
  • @JACK I suppose I should add that I considered a 1:1 swap-out like you suggest, instead of hoping that a smart switch will quickly pay for itself by letting me optimize when the pump runs (I use a “1 watt-year costs $1” rule-of-thumb). But if I just did a 1:1 swap-out, I’d just be labeling the wires and not going to such lengths to identify them. And without the need for identification, this whole question would be moot !-) – lionel Dec 10 '19 at 18:41
  • The two line wires are interchangeable as are the two load wires. You just have to label which are line and which are load. The smart switches for 240V double pole are fairly expensive compared to the Intermatic. I'm not sure a smart switch would quickly pay for itself. – JACK Dec 10 '19 at 19:40

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