All - in 2017 they seem to be making a bigger deal out of the dissimilar metals. We run into the case a ton where we run SS conduit through concrete and with a SS myers hub tie to a Painted Nema 4/12 box.(say Hoffman) We also have areas that require SS conduit (food processing) and when we enter an MCC room we change over to RMC and finish the conduit to panels or MCC's. Reading article 344.14 in the 2017 code makes me think we can not do this anymore. What are your thoughts? What are you doing to fix this issue?
2017 dissimilar metals - RMC with SS boxes
- Thread starter gilly
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Carultch
Senior Member
- Location
- Massachusetts
So where could I even use a standard die-cast zinc myers hub? Standard RMC conduit has bare steel threads, and steel is a different metal from die-cast zinc.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Who is 'they'?
Practically speaking there's no issue with connecting stainless steel to just about anything. In solar we use stainless steel to isolate copper from aluminum to prevent galvanic corrosion in spots that are totally exposed to the elements. Copper to aluminum is one of the most serious dissimilar metals situations you're likely to have.
At any rate, you are talking about connecting one kind of steel to another kind of steel. Those are not 'dissimilar', they are similar and very near the same.
when I was saying THEY - I ment the code panel. in 334.14 (2017) there was an update to this article. "Stainless steel RMC shall only be used with Stainless steel fittings and approved accessories, outlet boxes and enclosures." The Code panel also made a point to call out that you can use alumn with Galvanized steel fittings, then goes into Stainless steel quote. I might be reading this wrong but the way I am reading it you can only use Stainless steel conduit with Stainless steel fittings and boxes, so not connecting to GRC or Nema 4 painted steel boxes. I guess what I am wondering is in the picture I have attached does this violate code article 344.14 (2017)?
Attachments
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
Who on the code panel is a chemist, or where are they getting that info from?
??
i'd say they are quite different.
SS (passive) and plain 'ol steel is on opposite side of galvanic neutral line. SS to AL even worse. question is, how bad are those reactions.
??
i'd say they are quite different.
SS (passive) and plain 'ol steel is on opposite side of galvanic neutral line. SS to AL even worse. question is, how bad are those reactions.
Last edited:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The way I read it that sentence states that the fittings need to be stainless, everything else approved.
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
its a problem with their English grammar. the sentence as written implies two things:
1) SS RMC shall only be used with SS steel fittings
and
2) SS RMC shall only be used with approved accessories, outlet boxes and enclosures
#2 seems to suggest that the UL listings of "accessories", "outlet boxes" and "enclosures" should explicitly state "allowed to be attached to SS hardware"
if there was a galvanic concern, then #1 alone makes no sense.
then that begs the bigger Q, what the heck does #2 mean, where's the list of "approved" stuff, or did they mean "UL listed for use with SS" ??
Carultch
Senior Member
- Location
- Massachusetts
Yet most aluminum applications will have stainless fasteners as the de-facto selection. What else are you supposed to use? I don't understand how the galvanic chart is supposed to work.
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
why are most AL applications using SS fasteners??
zinc or galvanized steel fasteners are a better choice when attaching to AL. cheaper too.
the reaction charts are plentiful online.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
All I know is that racking systems that are listed for providing bonding all use stainless steel fasteners with aluminum. And in my experience galvanized fasteners seem to rust way too fast. (And no, I'm not talking about zinc-plated, although those obviously are a bad choice.)
As for the reaction charts, it seems to make a huge difference if 304 SS is 'active' or 'passive'. I admit to not really understanding what that means. I did pretty well in chemistry class but didn't get to any advanced level.
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
99.99-100% of your use of SS will be in passive mode.
other applications using SS may have it in active mode.
Carultch
Senior Member
- Location
- Massachusetts
What is active and passive mode? How do I know if a particular material/component is in active or passive mode?
RMC PVC Coated Stainless NEMA 4X still confused
RMC PVC Coated Stainless NEMA 4X still confused
I've read through this thread and am still confused.
We are on projects now that are spec'ed RGS with 316SS hardware and strut
I've got one that is spec'ed stainless exterior locations and RGS interior locations
And another that is NEMA 4X 316 SS boxes and enclosures with PVC Coated Rigid.
What I get out of the 2017 NEC is none of this meets code.
How do we change from one metal to another if they aren't allowed to come into contact?
I agree that the grammar makes the rule unclear, but sure looks to me like they are saying if any part of the system is stainless then the entire installation must be stainless.
RMC PVC Coated Stainless NEMA 4X still confused
I've read through this thread and am still confused.
We are on projects now that are spec'ed RGS with 316SS hardware and strut
I've got one that is spec'ed stainless exterior locations and RGS interior locations
And another that is NEMA 4X 316 SS boxes and enclosures with PVC Coated Rigid.
What I get out of the 2017 NEC is none of this meets code.
How do we change from one metal to another if they aren't allowed to come into contact?
I agree that the grammar makes the rule unclear, but sure looks to me like they are saying if any part of the system is stainless then the entire installation must be stainless.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
never mind
shortcircuit2
Senior Member
- Location
- South of Bawstin
This link has some information from NEMA...
https://www.nema.org/Technical/Docu...l Conduit and Electrical Metalling Tubing.pdf
I suggest contacting your NEMA representative for guidance.
https://www.nema.org/Technical/Docu...l Conduit and Electrical Metalling Tubing.pdf
I suggest contacting your NEMA representative for guidance.
shortcircuit2
Senior Member
- Location
- South of Bawstin
Then there is a PI No. 2709 by NEMA for 2020 on the confusion from the 2017 language in 344.14
Here is the proposed PI language...
344.14 Dissimilar Metals.
Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action.
Stainless Steel and Aluminum fittings and enclosures shall be permitted to be used with galvanized steel RMC, and galvanized steel fittings and enclosures shall be permitted to be used with aluminum RMC where not subject to severe corrosive influences.
Stainless steel rigid conduit shall only be used with:
1. stainless steel fittings
2. stainless steel boxes and enclosures
3. Steel (galvanized, painted, powder or PVC coasted, etc.) boxes and enclosures when not subject to severe corrosive influences
4. stainless steel, non-metallic, or approved accessories
Here is the substantiation for the PI...
Statement of Problem and Substantiation for Public Input
There has been confusion in the field in regards to what fittings can be used to transition from stainless steel RMC to galvanized RMC. This proposal is being made to make it clear that you can use stainless steel fittings, and enclosures with galvanized steel RMC but galvanized fittings should not be used with stainless steel RMC.
Here is the proposed PI language...
344.14 Dissimilar Metals.
Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action.
Stainless Steel and Aluminum fittings and enclosures shall be permitted to be used with galvanized steel RMC, and galvanized steel fittings and enclosures shall be permitted to be used with aluminum RMC where not subject to severe corrosive influences.
Stainless steel rigid conduit shall only be used with:
1. stainless steel fittings
2. stainless steel boxes and enclosures
3. Steel (galvanized, painted, powder or PVC coasted, etc.) boxes and enclosures when not subject to severe corrosive influences
4. stainless steel, non-metallic, or approved accessories
Here is the substantiation for the PI...
Statement of Problem and Substantiation for Public Input
There has been confusion in the field in regards to what fittings can be used to transition from stainless steel RMC to galvanized RMC. This proposal is being made to make it clear that you can use stainless steel fittings, and enclosures with galvanized steel RMC but galvanized fittings should not be used with stainless steel RMC.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Very roughly:
The 'galvanic series' basically tells you the voltage level that you get when you put two metals together. The farther apart two metals are on the galvanic series, the greater the voltage and the greater the chance of reaction.
When you have two different metals put together, one will get corroded and the other will be protected. This is why 'sacrificial anodes' are used on things like water heaters and boats. You have intentional galvanic corrosion to a disposable part.
For slightly dissimilar metals, the size of the components is relevant; for example you can have fasteners protected by the bulk metal since the amount of corrosion of the bulk is small, but you don't want your fasteners to corrode while protecting the bulk metal.
-Jon
The 'galvanic series' basically tells you the voltage level that you get when you put two metals together. The farther apart two metals are on the galvanic series, the greater the voltage and the greater the chance of reaction.
When you have two different metals put together, one will get corroded and the other will be protected. This is why 'sacrificial anodes' are used on things like water heaters and boats. You have intentional galvanic corrosion to a disposable part.
For slightly dissimilar metals, the size of the components is relevant; for example you can have fasteners protected by the bulk metal since the amount of corrosion of the bulk is small, but you don't want your fasteners to corrode while protecting the bulk metal.
-Jon
- Status