# WWYD: Wet core drilling over an energized 480v Nema 1 MCC



## guest (Feb 21, 2009)

Got a good safety question for you guys here:

My boss and j-man have decided that I am a pretty good core drill operator (had to drill 20 holes in a vault and 4 thru a 18" thick building wall) so they would like me to take on the next project:

We need 26(!) 3" holes cored through the 18" thick wall of a building. 

The problem? 

They are ALL directly above a 480v MCC with 500hp VFD's (3) and this is a NEMA 1 enclosure. 

The MCC's run aeration blowers that pretty much cannot be shut down for the length of time the drilling will require. 

The thickness of the wall means each hole takes several minutes (and several gallons of water to the core bit and running down the wall) to do. 

The j-man says just cover the MCC in plastic, with duct tape sealed to the wall and it will be ok.  The wall is painted cinderblock on the side I will be drilling from and we all know how well tape will seal to that. 

Access is tight so the possibility of ripping the plastic (or loosening it from the wall) is pretty high. 

The boss man and I haven't discussed this yet, but my position is that it is way too unsafe to do without a shutdown (and even then there is risk of problems on startup if enough water does manage to get into the MCC.) and that this is best hired out to a coring company with one of the drills that has a vacuum extraction for the core bit to minimize the water coming down the wall. (plus they could do the job a LOT faster that I can.) 

I have seen the aftermath of water intrusion into an MCC (Procter and Gamble plant in Long Beach, CA.) some years ago and it was really bad..including fatalities. 

I do not wish to experience that kind of incident first hand. 

So, what would you do?


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## ponyboy (Nov 18, 2012)

Sub out if possible

But if I had to id have a guy running a vac right next to the core bit to help with water. I'd also rig a catch basin over the gear and suspended from the ceiling that could catch water and any cores that fell. Plastic off the gear and empty the catch basin every few holes. Also run a hose to the drilling spot because water canisters suck


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## glen1971 (Oct 10, 2012)

Is it possible to hoard the gear with a system to get rid of the water? Plywood and sealed? If not, it would be shutdown time.. If they won't work with an outtage after the risks, hazzards and mitigation have been thoroughly discussed, that should shed some light on their view of safety and the value of the people involved with the job.. I'd decline to introduce any water near the gear, either by our crew coring or a sub coring...


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## drewsserviceco (Aug 1, 2014)

My Hilti has a port on it that I can attach a shop vac to it and it pulls air through the inside of the bit. Kinda like the water but in reverse. This cools the bit and keeps the teeth clear. I got it for tricky applications like you describe. Went in to job before they were open for business and cored 4 holes in an occupied office for furniture poke throughs. Holes cored and hardly any cleanup in less than an hour.


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## ponyboy (Nov 18, 2012)

If these 26 holes were clustered I'd think about just having a square piece of wall cut out, a wall sawing company could probably handle that dry or with minimal water. Then I'd have steel plates made with the holes lasered in and screw one to each side. You could put one side on and stub the pipes through then spray foam the void and put the other side on


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## Pete m. (Nov 19, 2011)

This is one that I would want to hire out. If there is no possibility of a shut down let a coring company assume the risk (better they have to make an insurance claim than your company).

Pete


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## Cow (Jan 16, 2008)

When I've subbed out core drilling in the past and water retention was important, the core driller has used a vacuum with what looked liked a donut attachment on the end of his hose. The core bit drilled through the center of the donut while the outside caught all the water around the hole. It seemed to work pretty well from what I remember.


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## B-Nabs (Jun 4, 2014)

I would sub it out, but on the subject of protecting the MCC, I think a piece of sloped plywood over the top of the unit, then with plastic draped over, and taped to the wall would be a great help. The plywood would serve to catch the cores if they fell through and let them roll off without damaging the plastic. I would probably use a very heavy duty tarp over the plywood and then maybe some very thick poly. As far as the taping goes, I would apply spray adhesive to the wall, then use that thick white plastic tape the shrinkwrap guys use when they're doing hazmat containment. That stuff really sticks, especially with pre-applied spray glue on the cinder block. Arrange the plastic in such a way that any water that does get through is directed to one particular area (away from MCC obvs). I would do all that whether or not the unit were shut down.


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## MDShunk (Jan 7, 2007)

Use plastic and "mastic tape", not duct tape. Shop vac operator to catch most of what he can at the point of drilling. Funnel the plastic into a barrel if you can. You'll be fine.


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## dawgs (Dec 1, 2007)

Hire it out. I just subbed out 24 4" holes in a 12" slab. It cost me $52 per hole. I can't rent the machine, rent the bit and provide labor for that. It's a no braineer.


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## 360max (Jun 10, 2011)

Pete m. said:


> This is one that I would want to hire out. If there is no possibility of a shut down let a coring company assume the risk (better they have to make an insurance claim than your company).
> 
> Pete


...your still not liability free, what does a core co. know about energized gear......nothing. They will have to rely on your expertise when safeguarding the gear.


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## 360max (Jun 10, 2011)

...if its block wall, why not dry core it?


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## Cow (Jan 16, 2008)

dawgs said:


> Hire it out. I just subbed out 24 4" holes in a 12" slab. It cost me $52 per hole. I can't rent the machine, rent the bit and provide labor for that. It's a no braineer.


I agree with that. 

A few weeks ago I had some holes cored. The core driller showed up right at 7 am and left some time after 4 or 5 that day, and did 35-40 holes from 1"-12" for $1145. You can't beat the price and efficiency of subbing it out.

Something else that gets overlooked as well, if you sub it out, that means you can get something else done at the same time. Lately, it seems like every little bit helps when you have deadlines.


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## Southeast Power (Jan 18, 2009)

Sub it out or not, you are going to want to take as much time as you can prepping the top of the MCC as you can.
If your shop has a rig, why not do it in house?


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## pete87 (Oct 22, 2012)

I saw a Super Computer get taken out that exact way ... Core Drilling on Top .

Code Blue and get the heck out of the way of the doors ... 6 man crash team on loco , hit those doors feet first .

Not our Shop but those Non Union boys never worked for IBM again .



If you Sub it ... still could be sued ? If so I would take extra care so can not happen . I would take care anyway .Your name is on it . Everyone has to be on top with this .




Pete


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## pete87 (Oct 22, 2012)

drewsserviceco said:


> My Hilti has a port on it that I can attach a shop vac to it and it pulls air through the inside of the bit. Kinda like the water but in reverse. This cools the bit and keeps the teeth clear. I got it for tricky applications like you describe. Went in to job before they were open for business and cored 4 holes in an occupied office for furniture poke throughs. Holes cored and hardly any cleanup in less than an hour.




Air cooled core bore ? How long do your core bits last ?


Never seen it ... and don't believe it .




Pete


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## drewsserviceco (Aug 1, 2014)

Hilti DD-130. There's a specific Hilti bit as well, pretty sure it's just the tougher one that can handle rebar. The core drill has a port that you open up and attach a shop vac to. It's really the same principle: keep the teeth clear so you can continue to expose new diamonds on the bit.

I've only ever purchased 1 of the size bits I needed, and haven't had to replace them. (So I obviously have different sizes, and have the first and only one I bought in that size) Some have as many as 40 holes.

I should be clear that I try to baby my equipment since none of its cheap and it's my money (instead of the boss's)


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## pete87 (Oct 22, 2012)

drewsserviceco said:


> Hilti DD-130. There's a specific Hilti bit as well, pretty sure it's just the tougher one that can handle rebar. The core drill has a port that you open up and attach a shop vac to. It's really the same principle: keep the teeth clear so you can continue to expose new diamonds on the bit.
> 
> I've only ever purchased 1 of the size bits I needed, and haven't had to replace them. (So I obviously have different sizes, and have the first and only one I bought in that size) Some have as many as 40 holes.
> 
> I should be clear that I try to baby my equipment since none of its cheap and it's my money (instead of the boss's)




Are we talkin 3" , 4" , 6 " holes ???

Or drilling just a 7/8 hole ? With a solid bit that vacs the dust ?



Pete


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## pete87 (Oct 22, 2012)

Just googled it ...


I would not of thought it possible with out water cooling .

Have not core bored since the 70's .

Cool .




Pete


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## splatz (May 23, 2015)

I voted only if it could be shut down, but it's hard to say. Some days I am dumber than others. Hard to really say without seeing it. If you don't feel it's safe it probably isn't. 

I have had very good luck with dry core bits for horizontal holes. I am told they won't go through rebar though, or will go through very slowly and ruin the bit. They go through block like butter. 

I am sure you already thought of this, but could you drill pilot holes through and drill the cores from the other side? 

Be sure to let everyone, even the customer, know you're concerns. I'd say 99% of the time if you think a little there's a safe way to do things. It may involve working on a Sunday, but so be it. Maybe you hire for guys and four drills so it goes faster and and the equipment can be turned off. Maybe you can drill the holes between the MCCs rather than above, maybe you can route what you're installing differently so you don't have to drill that wall. etc.


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## macmikeman (Jan 23, 2007)

Custom made oversized pull box located at or close to ceiling elsewhere in the room, pipe from that over to your live equipment and live to see another day. Anything else is just stupid and bad engineering.


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## KennyW (Aug 31, 2013)

ponyboy said:


> If these 26 holes were clustered I'd think about just having a square piece of wall cut out, a wall sawing company could probably handle that dry or with minimal water. Then I'd have steel plates made with the holes lasered in and screw one to each side. You could put one side on and stub the pipes through then spray foam the void and put the other side on
> 
> 
> Sent from my iPad using Tapatalk


Yes I agree, if it's a cinder block wall, get some blocks removed, way better plan.


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## Jarp Habib (May 18, 2014)

Cow said:


> I agree with that.
> 
> A few weeks ago I had some holes cored. The core driller showed up right at 7 am and left some time after 4 or 5 that day, and did 35-40 holes from 1"-12" for $1145. You can't beat the price and efficiency of subbing it out.
> 
> Something else that gets overlooked as well, if you sub it out, that means you can get something else done at the same time. Lately, it seems like every little bit helps when you have deadlines.


My company owns a small fleet of wet core machines so that cost is sunk already. Now I see why they have us run 'em instead of subbing that out holy cow. I know they aren't paying me a grand a day to do that. Fifty bucks a core times...300? 500? Somewhere in there. I'm in the wrong trade.

Were I to set up the operation described over a mission critical hazard like that, I would use an aforementioned vacuum setup, plastic sheeting on the opposite side around the machinery and an assistant with a catch bucket standing by. Any pilot holes would be foam plugged. I would *also* set up the core machine to core upwards by between 5°-10° to ensure that the majority of the water up until final penetration runs back toward the outside without affecting how level the future conduit is run.

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## CGW (Oct 14, 2014)

Sub it out. This might not be the same thing, but my boss took a job with a car collector (retired old-school GM bigwig who had like 20 classic cars in his garage) where we had to cut through a blast resistant hollow wall to supply power to an industrial auto paint unit, e-coat, clear coats, ventilation, etc. The guy's garage for these cars was built like a freaking vault. After inspection the owner was told we'd subcontract out cutting up the wall as it was so highly specialized. 

The good part was we got to help move all the cars


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