If the service to a 3 phase fire protection pump that is in a designated shed is a 480 volt, ungrounded, 3 wire Delta, and a transformer is installed for lighting and convenience receptacles, should you drive a ground rod at the shed and connect it to the transformer and a disconnect located in the shed, which would bond the lighting panel/disconnect/meter base on the shed's outer wall? Or would this cause issues with things, including the metering? Should everything just stay ungrounded?
3 wire Delta
- Thread starter mobo
- Start date
- Status
Basically, the only difference between bonding of a grounded and ungrounded system is the latter does not have a main/system bonding jumper. With respect to a service, there is no grounded conductor on the supply side of a service disconnecting means with which to bond, so you have to run an equipment bonding jumper to ground any "parts" on the NEC side of the service point.
There is a ground rod driven at the shed that has a ground running off it to a main disconnect that then jumpers to the lighting transformer and panel, and out to the meter socket . Is this proper? or can it cause issues?
One reason I ask is because at the meter socket I am getting what I feel are strange voltage readings to the equipment ground they ran to the socket from the ground rod. I'm getting, like, 370V on one phase to ground, 288 on another phase to ground, and 279 on another phase to ground.
- Location
- Illinois
- Occupation
- retired electrician
That is common on an ungrounded system and those voltages will change with a change in load.
OK, thank you. But as far as the grounding done inside the shed, no issues?
Well, barring size details and other than not having two rods (one's fine if measured at not more than 25 ohms to remote earth), sounds right.
Ok, thanks. The ohms are under the 25 ohm stipulation.
Tom the lectrician
Member
- Location
- Pennsylvania
I would make that change, bro
I would make that change, bro
Yeah, ground the transformer and the disconnect together and tie it into your ground rod. If you dont, you'll get wacky voltages for your lighting and receps. You'll see, like 80 on line and 25 on neutral. It's goofy, yes I would definately bond that transformer, and ground your motor. There should be a place for a screw somewhere in the picker head. It's a little service, so wire it like one. Al.ost all transformers should be bonded to stabilize your voltage, line to neutral and line to ground. Especially if you're using single phase devices on the secondary. I would bond
it for sure. How big is the xfmr in va? Gotta be a good 2 or 3 kva, right? Just enough to burn some lights and provide a 15 a recep?maybe 2 perhaps? Also, the proper way is according to 250, all over the place. You know the situation better than I do, but your answers are right there. If you're not sure where to bond your xfmr, let me know. Is it single phase or 3 phase? What size wire feeding it and how many va is it. Aeriously, you're gonna have issues on that deal, bro
I would make that change, bro
Yeah, ground the transformer and the disconnect together and tie it into your ground rod. If you dont, you'll get wacky voltages for your lighting and receps. You'll see, like 80 on line and 25 on neutral. It's goofy, yes I would definately bond that transformer, and ground your motor. There should be a place for a screw somewhere in the picker head. It's a little service, so wire it like one. Al.ost all transformers should be bonded to stabilize your voltage, line to neutral and line to ground. Especially if you're using single phase devices on the secondary. I would bond
it for sure. How big is the xfmr in va? Gotta be a good 2 or 3 kva, right? Just enough to burn some lights and provide a 15 a recep?maybe 2 perhaps? Also, the proper way is according to 250, all over the place. You know the situation better than I do, but your answers are right there. If you're not sure where to bond your xfmr, let me know. Is it single phase or 3 phase? What size wire feeding it and how many va is it. Aeriously, you're gonna have issues on that deal, bro
Last edited:
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Phase to neutral voltages should not depend on whether or not the neutral is grounded.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I agree, and even will claim they will not depend instead of should not depend on the neutral being grounded. That line to neutral voltage will remain 120 even if you grounded one of the lines instead of the neutral, you need to change the number of turns in the coil or change the primary input voltage to change the voltage between those two points. Only time you will see varying voltages to a supposedly grounded object is if that object is not bonded or there is a significant resistance or impedance in the bond path, but current must be flowing to have a voltage drop as well.
- Status