origineng (Customer) asked a question.
I am using PH50MGJ to step down 208V to 120V. The terminals that I am attaching my 208 legs (L1 & L2) have continuity. As a result, there is continuity between L1 and L2 at my two thermal protectors going to the motors. Is this OK? I always though L1, L2, and L3 should be isolated.
Here is a photo. I am connecting my two 208 legs to terminals 1-2. I am getting continuity at those terminals with nothing connected.
If you are using an Ohmmeter to find continuity through a transformer coil, that is normal. It is just a piece of wire. A really thin, long piece of wire in a coil. When an Ohmmeter is applying a low DC voltage to it, there is very little measurable resistance. This changes when you apply AC voltage due to the impedance of the coil and iron core and the other coil in close proximity.
Carefully check your wiring and measure the incoming voltage to make sure it matches your expectations before throwing the juice to it and it should be fine.
Per the wiring as shown in the photo, you should not have continuity between L1 and L2 on either of the motor protectors, because the wires are disconnected from the transformer's primary winding terminal screws (H1 and 208V). But when you connect those wires to the transformer's primary winding (H1 and 208V), you will get continuity between L1 and L2 on both of the motor protectors, because you have continuity from L1 to terminal block, to fuse, thru fuse to H1 screw, thru primary winding to 208V screw, to fuse, thru fuse, to terminal block, to L2. If you have continuity between L1 and L2 when the transformer primary is disconnected, then you have a problem, a wiring mistake, a short. I guess you did not yet install the 3-phase supply to the terminal blocks.
Since you mention "Newbie", hope you will find some suggestions helpful.
Looking at your back panel, may I suggest the following:
* use star washers under the DIN rail mounting screws, or better, use screws that have the star washer included, these will provide more even mounting pressure, stay more secure, and improve grounding.
* use accessory surge suppressor blocks on contactor coils, blocks have tabs that connect under coil screws and snap onto the contactor.
* use end blocks on both sides of terminal blocks to better secure the terminal blocks.
* use wire numbers to match wire numbers shown on schematics.(this would be required if being inspected to meet standards; UL, ETL, CSA).
* use mounting base and link module to mount motor protector and contactor. This makes wiring much easier. And the assembled unit has a higher SCCR.
* on some pressure-plate connections, like control transformers, using ferrules prevents fraying wire strands.
@K Price (Customer) That is correct. With the transformer disconnected (as shown), I have no continuity between L1 and L2. When I connect the transformer, I get continuity. Sounds like this is correct.
I have not wired in the 3-phase supply, yet. I am in the process of double and triple-checking everything before I do so. No room for error on this project.
I appreciate the additional advice. That all makes sense. I wish I had seen the link modules. It would have made things much cleaner and faster.
Thanks again!
Per the wiring as shown in the photo, you should not have continuity between L1 and L2 on either of the motor protectors, because the wires are disconnected from the transformer's primary winding terminal screws (H1 and 208V). But when you connect those wires to the transformer's primary winding (H1 and 208V), you will get continuity between L1 and L2 on both of the motor protectors, because you have continuity from L1 to terminal block, to fuse, thru fuse to H1 screw, thru primary winding to 208V screw, to fuse, thru fuse, to terminal block, to L2. If you have continuity between L1 and L2 when the transformer primary is disconnected, then you have a problem, a wiring mistake, a short. I guess you did not yet install the 3-phase supply to the terminal blocks.