Debate over RMC

[brother]

in the NEC 2008 they tried to elaborate a little over RMC 344.10 I know in the past we've always used pvc underground (direct burial) and stubbed up to rigid for protection to our boxes. If for any reason the rmc had to contact the earth cause of the pvc was a little lower, we would put a little tape around it to help deter the corrosion.

Well this is the (friendly) debate with a buddy, I say it was a good practice but not required. He says it WAS required, because of 344.10(A)(4) ferrous raceways cannot be protected by enamel only.

I say because of the way the galvanized steel rigid is made, (it has zinc in it) its NOT protected solely by enamel, so therefore it CAN be in direct contact with the earth.

Ok, so whos right??, Ive never really thought about this all these years, just took things for granted. forgive me if i sound dumb.

 

[roger]

in the NEC 2008 they tried to elaborate a little over RMC 344.10 I know in the past we've always used pvc underground (direct burial) and stubbed up to rigid for protection to our boxes. If for any reason the rmc had to contact the earth cause of the pvc was a little lower, we would put a little tape around it to help deter the corrosion.

Well this is the (friendly) debate with a buddy, I say it was a good practice but not required. He says it WAS required, because of 344.10(A)(4) ferrous raceways cannot be protected by enamel only.

I say because of the way the galvanized steel rigid is made, (it has zinc in it) its NOT protected solely by enamel, so therefore it CAN be in direct contact with the earth.

Ok, so whos right??, Ive never really thought about this all these years, just took things for granted. forgive me if i sound dumb.

You are right.

Roger

 

[infinity]

I say because of the way the galvanized steel rigid is made, (it has zinc in it) its NOT protected solely by enamel, so therefore it CAN be in direct contact with the earth.

I agree with Roger, RMC is already galvanized coated so it is permitted by 300.6(A)(3) to be in direct contact with the concrete. In some places they call it Galvanized Rigid Conduit or GRC.

 

[charlie]

You may find this interesting in the UL White Book, in my opinion, the rest of your code book.

"Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection.

​

In the absence of specific local experience, soils producing severe corrosive effects are generally characterized by low resistivity (less than 2000 ohm-centimeters).
​

Wherever ferrous metal conduit runs directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.​

Conduit that is provided with a metallic or nonmetallic coating, or a combination of both, has been investigated for resistance to atmospheric corrosion. Nonmetallic outer coatings that are part of the required resistance to corrosion have been additionally investigated for resistance to the effects of sunlight."​

This is found under RIGID FERROUS METAL CONDUIT (DYIX)

 

[ceb58]

I agree with Roger, RMC is already galvanized coated so it is permitted by 300.6(A)(3) to be in direct contact with the concrete. In some places they call it Galvanized Rigid Conduit or GRC.

Sorry guys but after working in a galvanizing plant for over 15 years I must. The pipe is not galvanized coated. Galvanizing is the term used for bonding the zinc to the metal. The coating is the same as what is on ground rods. The steel is submersed in molten zinc (850 deg f ) when the steel reaches the same temp. the zinc bonds to it.

I say because of the way the galvanized steel rigid is made, (it has zinc in it) its NOT protected solely by enamel, so therefore it CAN be in direct contact with the earth.

 

[iwire]

Sorry guys but after working in a galvanizing plant for over 15 years I must. The pipe is not galvanized coated.

Sorry I am going to go with UL on this one. :smile:

 

[don_resqcapt19]

Sorry guys but after working in a galvanizing plant for over 15 years I must. The pipe is not galvanized coated. Galvanizing is the term used for bonding the zinc to the metal. The coating is the same as what is on ground rods. The steel is submersed in molten zinc (850 deg f ) when the steel reaches the same temp. the zinc bonds to it.

It appears that is exactly how conduit is protected...the hot dip process.

Allied RIGID is hot-dipped galvanized inside and out.

 

[ceb58]

Sorry I am going to go with UL on this one. :smile:

:-?:-?:-?
Ferrous metal (pipe) + non-ferrous zinc = galvanized pipe

 

[acrwc10]

Just don't forget to protect the cut threads at the fittings.

 

[220/221]

Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection.

We have some kind of killer soil in AZ.

Back in the mid 70's, they started requiring additional protection (20 mils of tape). I thought is was NEC rules but have since learned it must be local.

Here is a typical example of un protected rigid. This is in an area with NO water except the 7" of anual rainfall. In a watered grassy area it wouldn't last 3 years. The metal is almost completly gone at grade level.

 

[brother]

Interesting comments. Its been said that the 'zinc' dip may not be enough for some areas.

Have any of you ever used pvc coated rmc??

 

[Cavie]

We have some kind of killer soil in AZ.

Back in the mid 70's, they started requiring additional protection (20 mils of tape). I thought is was NEC rules but have since learned it must be local.

Here is a typical example of un protected rigid. This is in an area with NO water except the 7" of anual rainfall. In a watered grassy area it wouldn't last 3 years. The metal is almost completly gone at grade level.

Same thing happens in Florida.

 

[Okie Sparky]

Have any of you ever used pvc coated rmc??[/QUOTE]

We do work in a gas plant and any GRC that is put in the ground is PVC-coated GRC. This plant has underground storage caverns and they use brine water to push the gas out of the caverns. They store the brine water in ponds and it has 98.9% salinity, although the ponds are lined with a liner to prevent a leak, the ground is very corrosive. Regular GRC doesn't last very long. Just the atmosphere by the brine ponds can be corrosive.

 

[brother]

Have any of you ever used pvc coated rmc??

We do work in a gas plant and any GRC that is put in the ground is PVC-coated GRC. This plant has underground storage caverns and they use brine water to push the gas out of the caverns. They store the brine water in ponds and it has 98.9% salinity, although the ponds are lined with a liner to prevent a leak, the ground is very corrosive. Regular GRC doesn't last very long. Just the atmosphere by the brine ponds can be corrosive.[/QUOTE]


Sounds like my buddy is right. The zinc doesnt give as much protection as i thought. pvc coated grmc probably should be required for direct contact with earth.