I have been doing a little work at a mining operation. I have been looking at the work that has been installed and have a few comments or questions.
Through out the mine area, they have 480 volt, 3-phase distribution. To obtain voltages needed for lights and tools and equipment, they have stepped down the voltage to 120/240 via a whole host of transformers. Most the nameplates on the transformers are 480 Delta, 120/240 Wye. From what I can gather, they are bringing down the equipment ground with the phase conductors when landing in the primary of the transformer. On the secondary side either at the transformer or the distribution panel they are providing a bonding jumper to bond the neutral to the enclosure. What I am not seeing at any of the separately derived systems is a grounding electrode or and electrode jumper going to building steel or any of the other made electrodes. My electrical theory on grounding is a little shaky, so I am trying to figure out all the danger with this. Everything is in solid rock, without building steel or waterlines.
This is what I come up with.
You have a grounding path via the 480-volt distribution.
But from the code, on the secondary, you need a main bonding jumper, a grounding electrode and conductor, and all grounded conductors at the source need to be bonded together.
One question: If this transformer is setting out in solid rock somewhere, and you don?t have any type of counterpoise run, what is my grounding electrode really going to do?? At this point, are we trying to equalize the potential to ground at the transformer. I can spout off what the code says, but without the electrical grounding theory behind it, I really don?t know what I am talking about. What kind of unsafe condition are these guys creating by not having any grounding electrodes in place around the site?
Through out the mine area, they have 480 volt, 3-phase distribution. To obtain voltages needed for lights and tools and equipment, they have stepped down the voltage to 120/240 via a whole host of transformers. Most the nameplates on the transformers are 480 Delta, 120/240 Wye. From what I can gather, they are bringing down the equipment ground with the phase conductors when landing in the primary of the transformer. On the secondary side either at the transformer or the distribution panel they are providing a bonding jumper to bond the neutral to the enclosure. What I am not seeing at any of the separately derived systems is a grounding electrode or and electrode jumper going to building steel or any of the other made electrodes. My electrical theory on grounding is a little shaky, so I am trying to figure out all the danger with this. Everything is in solid rock, without building steel or waterlines.
This is what I come up with.
You have a grounding path via the 480-volt distribution.
But from the code, on the secondary, you need a main bonding jumper, a grounding electrode and conductor, and all grounded conductors at the source need to be bonded together.
One question: If this transformer is setting out in solid rock somewhere, and you don?t have any type of counterpoise run, what is my grounding electrode really going to do?? At this point, are we trying to equalize the potential to ground at the transformer. I can spout off what the code says, but without the electrical grounding theory behind it, I really don?t know what I am talking about. What kind of unsafe condition are these guys creating by not having any grounding electrodes in place around the site?
