Crane added 4th wire

Have a steel cutting plant that is having there cranes zipper rail replaced. Found several code problems that will be addressed. Crane operates on 3phase 480V The main Incoming service is 800Amp 3phase 240V. Several transformers scattered around building supply the 480V. Crane now operates on a aging 3 wire system and will be upgraded with a 4th ground wire. Art 610-61 entitled Grounding. The trolley frame shall not be considered as electrically grounded through the bridge or trolley wheels and it’s respective tracks. That’s how it is now
No problem completely understand the need for the 4th ground wire. However the last line in the article “A separate bonding conductor shall be provided” So can that be a simple jumper from the structured steel or do I need to carry the grounded XO terminal from the 480V transformer to the 4th crane ground wire. The 480 V transformer is currently bonded to the structured steel I beam. Surface lug on outside of transformer to lug on I beam. #2 jumper
I’m not sure if there trying to ground the crane or bond the track to the crane or both. The crane is operated from the ground by hanging handheld controls. It’s rides the length of the building.
 

anthonysolino

Senior Member
your bonding conductor is defined in chapter one, if you have the 2020 NEC its page 34 on the left side. from what it seems, the language is requesting a conductor that jumps between the metal parts. as a result of this connection your 610 reference would make the installation compliant being, that jumper to the "Metal to metal bearing surfaces" are now all considered to be electrically intimate at that point.
 
I’m assuming the 4th wire once installed will bond to the crane and make continues contact while it’s moving. (Equipment side) My question is how is that 4th wire grounded on the line side if you will. Is it a ground or a bond. The more I read the more exceptions or the more confusing it gets. Some text like OSHA never mention ground they mention bond only. NEC mentions both. I just want it to be safe and done correctly. Because right now I’m not sure where I’m running this ground/bond from. Ty
 

anthonysolino

Senior Member
where does the circuit originate for the crane? a transformer? if so there should be a terminal on the inside, where all the EGC's go from the primary and secondary, it seems the conductor would bond at this point, I would NOT bring this wire to the XO, being this is not a neutral conductor. you don't want your fault return path going through the XO. I am not much of an engineer but I believe you would not trip the overcurrent device in this fashion. as for the building steel that wouldn't accomplish to much of any thing.you do NOT want all these parallel paths to earth all over the place.normal rules permit the EMT to be used as an EGC in this case however it appears the language is requesting an EGC from the source to the load which makes sense if you think about it. thats how I would interpret this, IF it was me, I would go all the way to the source and pull and EGC in every conduit all the way to the crane. that way you have an effective, low impedance path back in the event of a fault.
 
Last edited:

anthonysolino

Senior Member
I’m assuming the 4th wire once installed will bond to the crane and make continues contact while it’s moving. (Equipment side) My question is how is that 4th wire grounded on the line side if you will. Is it a ground or a bond. The more I read the more exceptions or the more confusing it gets. Some text like OSHA never mention ground they mention bond only. NEC mentions both. I just want it to be safe and done correctly. Because right now I’m not sure where I’m running this ground/bond from. Ty
[/QUOT
You do not need an EGC is the wiring in metal conduit. The conduit itself is the EGC.
Back in 358 for EMT it permits this but read the language in 610 it seems to be instructing you to do other wise. he cant simply jump to the building steel, as a fault path, I guess he could find a fitting for the outside of the conduit and round a bonding jumper back to the 4th rail on the crane but then if the EMT goes to a transformer which probably has FMC ran to it he needs to make sure theres a EGC installed in all the raceways back to the source.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
610.61 looks like what is under discussion. The way I read it the moveable part of the crane is considered equipment grounded by the steel bearings and wheels that ride on the track/frame, but stationary part of the crane need to be _bonded_ in such a way that all the metal parts are solidly connected together so if any part of the frame becomes energized it will cause a breaker to trip. This can be done with nuts and bolts or with wire jumpers whatever is effective or appropriate.

This is related to, but not the same thing as, an Equipment Grounding Conductor which could be either metal conduit or a wire type and would be part of the wiring that brings power to the crane. I don't see anything that requires running an extra conductor back to the transformer.
 

anthonysolino

Senior Member
610.61 looks like what is under discussion. The way I read it the moveable part of the crane is considered equipment grounded by the steel bearings and wheels that ride on the track/frame, but stationary part of the crane need to be _bonded_ in such a way that all the metal parts are solidly connected together so if any part of the frame becomes energized it will cause a breaker to trip. This can be done with nuts and bolts or with wire jumpers whatever is effective or appropriate.

This is related to, but not the same thing as, an Equipment Grounding Conductor which could be either metal conduit or a wire type and would be part of the wiring that brings power to the crane. I don't see anything that requires running an extra conductor back to the transformer.
the reason I mentioned a wire type EGC it because the language shoots you over to 250 part 5 and 7 I read though those and it gives you an allowance of what can be used to do so.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
...you don't want your fault return path going through the XO. I am not much of an engineer but I believe you would not trip the overcurrent device in this fashion.
Actually you do want your fault return path to go to the XO, that is how you clear a fault.

as for the building steel that wouldn't accomplish to much of any thing.you do NOT want all these parallel paths to earth all over the place.
You do want all the parallel paths you can get when it comes to fault current. You do not want parallel paths for neutral or grounded conductor current.

normal rules permit the EMT to be used as an EGC in this case however it appears the language is requesting an EGC from the source to the load which makes sense if you think about it. thats how I would interpret this, IF it was me, I would go all the way to the source and pull and EGC in every conduit all the way to the crane. that way you have an effective, low impedance path back in the event of a fault.
You likely have a low impedance path in case of a fault with just the steel and it looks like the code is just making sure that you add jumpers of some sort around any parts that may not be solidly connected. A wire in every conduit may be a good supplement where there is lots of vibration and wear and tear but it is no substitute for making sure your conduits are assembled rock solid.
 

anthonysolino

Senior Member
Actually you do want your fault return path to go to the XO, that is how you clear a fault.


You do want all the parallel paths you can get when it comes to fault current. You do not want parallel paths for neutral or grounded conductor current.


You likely have a low impedance path in case of a fault with just the steel and it looks like the code is just making sure that you add jumpers of some sort around any parts that may not be solidly connected. A wire in every conduit may be a good supplement where there is lots of vibration and wear and tear but it is no substitute for making sure your conduits are assembled rock solid.
I disagree I don't think you want your fault path to have to travel on the building steel, and 250 does not permit the use of building steel an alternative for equipment bonding, and taking that conductor straight the XO back at his service? or does he have a free standing transformer? will cause the fault current to travel through the center tap of the winding why would one want this? you want a LOW impeded fault path back to the source, how does going to the building steel going to the XO create a low impeded path? if any thing it would be higher doing like that. electrically you want a smooth flow back to the OD device to facilitate opening. building steel does not aid in causing a breaker to open in a fault.
I guess if you take the wire to the case of the transformer its the same being the SBJ is installed?
 
Last edited:

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
I disagree I don't think you want your fault path to have to travel on the building steel, and 250 does not permit the use of building steel an alternative for equipment bonding, and taking that conductor straight the XO back at his service? will cause the fault current to travel through the center tap of the winding why would one want this? you want a LOW impeded fault path back to the source, how does going to the building steel going to the XO create a low impeded path? if any thing it would be higher doing like that. electrically you want a smooth flow back to the OD device to facilitate opening. building steel does not aid in causing a breaker to open in a fault.
The XO in the transformer is the ultimate destination for the fault current through any of the Equipment Grounding Conductors that are a part of that electrical system. The neutral to ground bond is made at the XO inside the transformer or at the first disconnect.

610.61 is not talking about using the building steel as an equipment ground and neither am I. I'm not a crane guy so I could be a little off on some of the finer details, but the way I read it this section is talking about making sure all of the steel is bonded together so that if there is a fault anywhere on the crane it is carried back to the equipment grounding conductor that is ran with the other conductors that power the crane... that is what 250 parts V and Vii is all about.
 
Enjoying the back and forth and taking it all in. In this particular instance I’m dealing with a 3phase 3 wire transformer no neutral. The XO is being used as the egc and is then bonded to structure steel sitting right next to the transformer. 240primary 480V secondary wye no high leg feeding a panel board servicing several large saws and the crane rail. No load neutral is being used for any equipment. There replacing the old zipper rail and adding a forth ground rail that’s the whole job. This place is old and I’m slowly bringing things into this century starting with proper disconnects and labeling. I will know exactly where everything goes where it’s being fed from where my source ground is located after a 5pm shutdown and lock out tonight. Ty to all who have responded I will know a lot more after today. I was unable to shut anything down before today as this equipment runs round the clock. Stay tuned. As I mentioned before I really want this place and it’s employees to be safe. Right now there is no respect for the 480V all over the plant. No service disconnects or not many no signage no labels open holes in equipment no connectors on some someone is going to get hurt or worse.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Not anymore not since 1971 no longer acceptable to even run a three wire system. A 4th ground must be added.

You can have a ground wire and not ground one of the phases or neutral point. Unless you mean that after 1971 the circuit must be solidly grounded.
 
Was out there taking things apart trying to label things. 240V 3phase 5 wire (neutral and grd) with a high leg. 800Amp incoming main service. Two transformers one 240/480 feeds crane and a sub panel other side of building. another feeding several saws wired in reverse to get the 480V
Someone ran the 480V 3ph crane feeds from the 480V panel double tapped on a 3ph 30A breaker (4 cranes) ran there wire down thru troughs and nipples back into and thru the 240V panel which was the original rigid conduit feeding the crane. I’m pretty sure that 480V should not be sharing the same raceway as the 240V panel but nothing would surprise me anymore. I’ve decided to pull a # 6 stranded ground from the 240V incoming service entrance ground and take it right to the trolly 4th ground wire. The crane company asked for a ground wire a ground wire they will get. they might do additional bonding on there end. I will look into that when there done.
 
You can have a ground wire and not ground one of the phases or neutral point. Unless you mean that after 1971 the circuit must be solidly grounded.
Sorry that 1971 date was for the replacement of all zipper track steel to not be used. In 2005
OSHA incorporated NEC 610.6 for all overhead and gantry cranes which states the trolly frame and bridge shall not be considered as electrically grounded thru the bridge and trolley wheels and it’s respective tracks. A separate bonding jumper shall be provided. That’s where my brain started to hurt researching art 250 the entire crane monorail hoists metal parts of crane shall be bonded either by mechanical ( the conduit) or bonding jumpers so the entire crane is a ground fault path.
Ground fault path to where the building steel or ground fault path to earth ground. My thinking is I provide the crane company with a source ground wire they in turn attach to there 4th overhead wire and once the crane makes that connection it creates the bond needed for the ground fault path for the entire crane and no longer relies on the wheels as the crane bond.
 

anthonysolino

Senior Member
Enjoying the back and forth and taking it all in. In this particular instance I’m dealing with a 3phase 3 wire transformer no neutral. The XO is being used as the egc and is then bonded to structure steel sitting right next to the transformer. 240primary 480V secondary wye no high leg feeding a panel board servicing several large saws and the crane rail. No load neutral is being used for any equipment. There replacing the old zipper rail and adding a forth ground rail that’s the whole job. This place is old and I’m slowly bringing things into this century starting with proper disconnects and labeling. I will know exactly where everything goes where it’s being fed from where my source ground is located after a 5pm shutdown and lock out tonight. Ty to all who have responded I will know a lot more after today. I was unable to shut anything down before today as this equipment runs round the clock. Stay tuned. As I mentioned before I really want this place and it’s employees to be safe. Right now there is no respect for the 480V all over the plant. No service disconnects or not many no signage no labels open holes in equipment no connectors on some someone is going to get hurt or worse.

"The XO is being used as the egc and is then bonded to structure steel sitting right next to the transformer" dude I could be wrong but nothing about that seems safe, I hope someone chimes in here, but that transformer doesn't go straight to the utility why would you use the XO as an equipment ground I would have thought you would take that conductor straight to the EGC bonding terminal strip inside the transformer. the only thing that would go to that XO is the grounding electrode conductor and the jumper that goes from the XO to the EGC strip nothing else. if I am not mistaken you cant be pulling EGC's off the Xo's of transformers. our XO serves a different purpose than that of the utility world. idk man just something about that seems wrong I find it really hard to believe that the EGC going straight to a XO is going to clear a fault your not going to have enough fault current to open a breaker.
 

kwired

Electron manager
Location
NE Nebraska
Enjoying the back and forth and taking it all in. In this particular instance I’m dealing with a 3phase 3 wire transformer no neutral. The XO is being used as the egc and is then bonded to structure steel sitting right next to the transformer. 240primary 480V secondary wye no high leg feeding a panel board servicing several large saws and the crane rail. No load neutral is being used for any equipment. There replacing the old zipper rail and adding a forth ground rail that’s the whole job. This place is old and I’m slowly bringing things into this century starting with proper disconnects and labeling. I will know exactly where everything goes where it’s being fed from where my source ground is located after a 5pm shutdown and lock out tonight. Ty to all who have responded I will know a lot more after today. I was unable to shut anything down before today as this equipment runs round the clock. Stay tuned. As I mentioned before I really want this place and it’s employees to be safe. Right now there is no respect for the 480V all over the plant. No service disconnects or not many no signage no labels open holes in equipment no connectors on some someone is going to get hurt or worse.
What you described is a three phase 4 wire system. You happen to not be using the neutral for any loads but is still the grounded point of the system. All ground fault current will return to the XO terminal of the transformer regardless of what other items it finds a path through on it's way there.

All that content of 610.61 mentioned in OP is about is assuring there is a bond around the trolley in case there is too much resistance between the crane and the frame. If whatever cable method you have between crane and frame for the supply conductors contains a fourth conductor used as an EGC, that will make up the bonding jumper, they just don't want to rely on the trolley to have to provide low enough resistance to be effective ground fault path.
 
Top