Underground Mine Grounding

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Bigjabe

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Hi all, is anyone here familiar with grounding for an underground mine? I'm pretty sure the standard procedure is have your ground grid on the surface and run ground conductors down the shaft... but I was wondering has anyone put rods or plates actually down in the mine?

Thanks
 
I do a good bit of work in a limestone mine. We once had to run power to a previously unused area. We had them use their bolt drill to drill holes in the rock. We then put in ground rods with the holes stuffed full with brass and copper shavings that another customer let us have. Most of the work just gets checked during their regular MSHA visits, but the area AHJ wanted to look at this one and passed it.
 
Mines do not fall under the purview of the NEC so what do they fall under?

90.2(B) Not Covered. This Code does not cover the following:
(1) Installations in ships, watercraft other than floating build-
ings, railway rolling stock, aircraft, or automotive vehicles
other than mobile homes and recreational vehicles
Informational Note: Although the scope of this Code in-
dicates that the Code does not cover installations in ships,
portions of this Code are incorporated by reference into
Title 46, Code of Federal Regulations, Parts 110–113.
(2) Installations underground in mines and self-propelled
mobile surface mining machinery and its attendant
electrical trailing cable
Click to expand...
 
a basic mining power system
substation w/station ground grid (la's and surface equip frames are ties to this)
a ngr on the secondary mine power feed
the ngr low side is tied to a seperated and isolated ground bed (safety or neutral bed)
this is used for the mine grounding system
all xfmrs in the mine are ngr and tied to this
do not combine mine and surface power, each have their own xfmr

this is basically the law for underground coal mines
many deep non coal mines do the same
in Canada I believe it is similar
 
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Ingenieur said:
a basic mining power system
substation w/station ground grid (la's and surface equip frames are ties to this)
a ngr on the secondary mine power feed
the ngr low side is tied to a seperated and isolated ground bed (safety or neutral bed)
this is used for the mine grounding system
all xfmrs in the mine are ngr and tied to this
do not combine mine and surface power, each have their own xfmr

this is basically the law for underground coal mines
many deep non coal mines do the same
in Canada I believe it is similar
Click to expand...

Hmm, I’m basically doing that except for the LA’s and some surface infrastructure right at the shaft. there’s an overhead line going between the station sub and where the feeders to U/G go... where can I ground the LA’s and surface infrastructure? Is the isolated bed supposed to have nothing but the NGR tied to it?
 
Bigjabe said:
Hmm, I’m basically doing that except for the LA’s and some surface infrastructure right at the shaft. there’s an overhead line going between the station sub and where the feeders to U/G go... where can I ground the LA’s and surface infrastructure? Is the isolated bed supposed to have nothing but the NGR tied to it?
Click to expand...

only ug equip on the isolated bed
everything else (la's, equip frames, etc) on the station bed
some run a shield wire on the pole top tied to station and bond surface stuff to it
we typically do not use la's at the mine mouth since everything is insulated (inc the gnd)

what are you mining?
any ignition hazard?
you do not want a strike carried into the mine or raising the frame potential of ug equipmemt
or worse a substation primary ground fault to raise the mine equip frame potential
 
ActionDave said:
You'd be surprised what you can get away with electrically though. Rubber cords are the rule not the exception and they are strung out everywhere.
Click to expand...

every ckt has 3 levels of gf protection
is on a ngr system
redundant series sc protection
all egc's are monitored, if >3 Ohm trip the ckt
all cb's have uv coils
all plugs are interlocked, pull it a bit and a pilot ckt drops uv, can't open under load
cables are double insulated with bare grounds, more likely to gf if pinched
most equip has powered reel to play out/take up the cable to keep it out of the way
and only certified electricians can work on any of it

shocks are rare
90% are lock out / tag out violation
 
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