SCCR For Elevator

[jstandefer@e3electric]

Our customer is saying it is our responsibility as the electrical contractor to label our fused 35A 480V disconnect with a SCCR rating per the Elevator inspectors request. He says it is per NEC 110.24. The elevator controller only has a 5k SCCR and our electrical system is 10k. Everything I find is that the controller itself is not code compliant. Has anyone had this issue? How would I lower the SCCR rating of our disconnect?

 

[jim dungar]

How would I lower the SCCR rating of our disconnect?

You cannot change the rating of your disconnect.
What the inspector probably wants to know is how much short circuit amps are available at your disconnect switch. Has this calculation been done?

You maybe able to lower the amount of available fault current at the elevator controller. The easiest way is to add impedance by increasing the length of the feeder conductors or by adding a transformer.

But you should also see if the elevator controller has a series rating with a specific fuse type. This information can only come from the controller manufacturer.

 

[augie47]

They seem to be addressing a basic requirement of electrical installations but their terminology and Code references are not correct, 110.24 address service equipment marking and you can't "change" the SCCR of equipment.
Most likely what they want addressed is the available fault current at the elevator equipment to assure it is not higher than 5k.
If it's a designed job this should have been addressed by the engineer.

(Mr. Dungar answered as I was typing with a better explaination)

 

[don_resqcapt19]

Unless you are on the 2026 code, nothing in 110.24 would require the disconnect to be marked with the available fault current.

 

[Jraef]

Is it a fused disconnect? If not, then yes, it will only be rated 10kA. But if it is fused, it is usually going to be rated for the rating of the fuses, often 100kA or more!

The elevator equipment is another matter though, YOU cannot change the rating of it in the field, nor can you change the Available Fault Current by using fuses (as many people seem to think). IF the equipment manufacturer listed their equipment to have a Series Rating with specific fuses, then that's allowed to be outside of the unit itself, but you will need documentation of that from them. Generally though if they had that, they would have put it on their nameplate as per UL rules.

Everything I find is that the controller itself is not code compliant.

Well, TECHNICALLY, Code does not say that the equipment mfr has to deal with this, but Code does say that it cannot be CONNECTED to a system with more Available Fault Current than what the equipment is listed for. The real problem lies with the purchaser, who ALLOWED the elevator equipment supplier to get away with the "lazy" approach to the requirements for SCCR listings. UL allows a "courtesy" listing of 5kA with no testing and zero attention to component selection and listing, so that's likely what they did, essentially "kicking the can down the road" to whomever is installing it (in this case, you). So yes, MANY ECs are having to deal with this issue in the field, and there are no simple solutions. The REAL solution is a process of educating end users who are about to buy equipment that they must talk to their electricians FIRST and understand what they must DEMAND, in their purchase specifications, from the equipment vendors. I.e., "Elevator controller SHALL be UL listed with a minimum of 25kA SCCR" (or whatever value you have calculated that they need). That is a tough row to hoe however...

What Jim Dungar offered are likely your best options, but before you start buying anything, the first thing to do is DETERMINE what your Available Fault Current is at the disconnect you are providing, and if there is any appreciable distance from your disconnect to the elevator panel, what it is there. It's REMOTELY possible that, under the right conditions, you might have less than 10kA at your disconnect and less than 5kA at the elevator panel. Knowledge is power...

 

[Strathead]

Our customer is saying it is our responsibility as the electrical contractor to label our fused 35A 480V disconnect with a SCCR rating per the Elevator inspectors request. He says it is per NEC 110.24. The elevator controller only has a 5k SCCR and our electrical system is 10k. Everything I find is that the controller itself is not code compliant. Has anyone had this issue? How would I lower the SCCR rating of our disconnect?

As Jim said, and I will clarify, SCCR (short circuit current rating) is the rating of the equipment and defines the maximum allowable current at the equipment if it short circuits. AFC (available fault current)t is the maximum amperage the power source is capable of delivering at a point in the distribution system. This is a result of Ohm's law and is reduced even by small resistance changes like wire, so the longer the wire the lower the AFC. FYI AIC(ampere interrupting current) is the maximum current that a given breaker, fuse or switch can safely interrupt without fusing, melting or blowing up.

I have run in to the exact requirement you are dealing with here in Florida. Who is responsible depends on the specifications. Many jobs today require the gear supplier to do a coordination and short circuit study. If so, then the AFC at the elevator controller is a required part of this and will be included in that study. This is what the equipment gets marked at. If the study isn't required per the specifications, it is the Electrical Engineer's responsibility in my opinion. Now, if the AFC is higher than the controller, (and all of them are rated at 5K as far as I know), then it is always the Engineer's responsibility to determine the solution in my opinion, and one they are likely to try and pass off. I have had to solve it, but I charge for it. As stated, longer wire is the easy fix, but another solution is to install an isolation transformer in the circuit. It seems silly , but that is a big reason why they make 208 to 208 transformers. The other reason is for audio isolation, but that is another story.

 

[jim dungar]

....then it is always the Engineer's responsibility to determine the solution in my opinion, ....

Why?
If the AFC has been calculated at the equipment disconnect, shouldn't the person buying the equipment purchase the appropriate ratings?

I know when I performed studies, as a gear manufacturer, I was never provided with end use equipment ratings. Typically the third party equipment hadn't been purchased yet or, more likely, the electrical contractor just wanted the study done quickly so the service equipment could be ordered so they didn't provide enough information to study down to branch circuits.

 

[ron]

then it is always the Engineer's responsibility to determine the solution in my opinion, and one they are likely to try and pass off.

Why would the Engineer need to solve this if the buyer of the equipment didn't do their due diligence? The Engineer has no control of the end use equipment manufacturer's equipment and their ratings.

 

[JoeStillman]

...it is always the Engineer's responsibility to determine the solution in my opinion, and one they are likely to try and pass off.

Almost never does the engineer have Available Fault Current data from the utility company at the time of the design.

 

[Strathead]

To answer all three of you. This is my opinion based on experience. First off, I am referring to new construction. The elevator is a fairly easy one because I have done several, and my experience is that at least Kone, and Otis only have SCCR of 5000, they don't make their equipment with a higher SCCR and their standard instructions tell you this. Second, the Electrical Engineer and tell and order of magnitude AFC at points on the system, based on generic transformer impedances, conservative wire lengths, etc. Joe, I can pull up 20 sets of bid plans right now that include an AIC rating for fully rated distribution systems. Ron, in most cases the MEP's are all one engineering firm. THEY specify the equipment. If they didn't specify equipment with a high enough SCCR for the system designed by their brother engineer, that is their problem. If they cop out and require the mechanical bidder say, "provide SCCR as required" they are basically making the customer pay for equipment that has an excessive SCCR, because if the engineer can't make an educated estimate of the SCCR, then the mechanical estimator certainly isn't going to. Jim, my Engineer. who is out of Jacksonville specifically asks for any cut sheets for equipment that is 60A or larger and available. Here is a snip of a report from a recent report that I am now dealing with.

 

[ron]

To answer all three of you. This is my opinion based on experience. First off, I am referring to new construction. The elevator is a fairly easy one because I have done several, and my experience is that at least Kone, and Otis only have SCCR of 5000, they don't make their equipment with a higher SCCR and their standard instructions tell you this. Second, the Electrical Engineer and tell and order of magnitude AFC at points on the system, based on generic transformer impedances, conservative wire lengths, etc. Joe, I can pull up 20 sets of bid plans right now that include an AIC rating for fully rated distribution systems. Ron, in most cases the MEP's are all one engineering firm. THEY specify the equipment. If they didn't specify equipment with a high enough SCCR for the system designed by their brother engineer, that is their problem. If they cop out and require the mechanical bidder say, "provide SCCR as required" they are basically making the customer pay for equipment that has an excessive SCCR, because if the engineer can't make an educated estimate of the SCCR, then the mechanical estimator certainly isn't going to. Jim, my Engineer. who is out of Jacksonville specifically asks for any cut sheets for equipment that is 60A or larger and available. Here is a snip of a report from a recent report that I am now dealing with.


View attachment 2581533

The architect specifies the elevator in my world of design.

 

[Knightryder12]

As Jim said, and I will clarify, SCCR (short circuit current rating) is the rating of the equipment and defines the maximum allowable current at the equipment if it short circuits. AFC (available fault current)t is the maximum amperage the power source is capable of delivering at a point in the distribution system. This is a result of Ohm's law and is reduced even by small resistance changes like wire, so the longer the wire the lower the AFC. FYI AIC(ampere interrupting current) is the maximum current that a given breaker, fuse or switch can safely interrupt without fusing, melting or blowing up.

I have run in to the exact requirement you are dealing with here in Florida. Who is responsible depends on the specifications. Many jobs today require the gear supplier to do a coordination and short circuit study. If so, then the AFC at the elevator controller is a required part of this and will be included in that study. This is what the equipment gets marked at. If the study isn't required per the specifications, it is the Electrical Engineer's responsibility in my opinion. Now, if the AFC is higher than the controller, (and all of them are rated at 5K as far as I know), then it is always the Engineer's responsibility to determine the solution in my opinion, and one they are likely to try and pass off. I have had to solve it, but I charge for it. As stated, longer wire is the easy fix, but another solution is to install an isolation transformer in the circuit. It seems silly , but that is a big reason why they make 208 to 208 transformers. The other reason is for audio isolation, but that is another story.

I have never seen an engineer fix this problem. (unless they are getting paid) It is the 3rd party equipment suppliers responsibility to purchase the correct SCCR rated equipment. This is always an issue with chillers and large RTU/AHU's. It is the job of the engineer to inform the other trades of the AFC at equipment connection points prior to equipment being purchased. As far as equipment being rated at 5K that is just the manufacturer saving money and typically other SCCR rating are available. (At least this is what I have found to be true with equipment)

 

[Knightryder12]

To answer all three of you. This is my opinion based on experience. First off, I am referring to new construction. The elevator is a fairly easy one because I have done several, and my experience is that at least Kone, and Otis only have SCCR of 5000, they don't make their equipment with a higher SCCR and their standard instructions tell you this. Second, the Electrical Engineer and tell and order of magnitude AFC at points on the system, based on generic transformer impedances, conservative wire lengths, etc. Joe, I can pull up 20 sets of bid plans right now that include an AIC rating for fully rated distribution systems. Ron, in most cases the MEP's are all one engineering firm. THEY specify the equipment. If they didn't specify equipment with a high enough SCCR for the system designed by their brother engineer, that is their problem. If they cop out and require the mechanical bidder say, "provide SCCR as required" they are basically making the customer pay for equipment that has an excessive SCCR, because if the engineer can't make an educated estimate of the SCCR, then the mechanical estimator certainly isn't going to. Jim, my Engineer. who is out of Jacksonville specifically asks for any cut sheets for equipment that is 60A or larger and available. Here is a snip of a report from a recent report that I am now dealing with.


View attachment 2581533

As others have said, the MEP firm does not order or specify the elevator, that is the Architect.

 

[Strathead]

As others have said, the MEP firm does not order or specify the elevator, that is the Architect.

And it is the Electrical Engineer who is responsible to ensure his electrical design is adequate for the equipment provided by the architect. As I stated, I believe every elevator controller has an SCCR of 5000 amps. If it isn't all then it is most, so it is pretty easy for the Electrical Engineer to ensure no more than 5000 amps is available.

 

[Strathead]

It is the job of the engineer to inform the other trades of the AFC at equipment connection points prior to equipment being purchased.

THIS is where the rubber mees the road in my post. The Electrical and the Mechanical Engineers work for the same company. The specified HVAC units doesn't meet the AIC requirements of the design ON THE PERMIT Plans and Specs. The mechanical contractor supplies the equipment as specified, the electrical contractor installs the system per plans and specifications. Who is responsible when the Short Circuit Study report comes out and looks like the one I attached above?

 

[Strathead]

The architect specifies the elevator in my world of design.

And when you are three weeks from final inspection and the available current at the elevator exceeds the SCCR, who's job is it to fix it? For that matter, whose job was it to determine that the AFC was too high in the first place? (assuming there was nothing in the specifications that passed the buck to the electrical contractor)

 

[JoeStillman]

And it is the Electrical Engineer who is responsible to ensure his electrical design is adequate for the equipment provided by the architect. As I stated, I believe every elevator controller has an SCCR of 5000 amps. If it isn't all then it is most, so it is pretty easy for the Electrical Engineer to ensure no more than 5000 amps is available.

I just wish more electrical contractors understood that obtaining accurate fault data from the POCO is on the critical path upstream of ordering equipment. Our estimates of AFC are necessarily conservative because we don't want any re-work or change orders. It's in the contractors' interest to get us the data (or the power study submittal) early on. The AIC's could come down from our estimates, or we could get back to the elevator guys and tell them 5 kAIC doesn't cut it. AFC is not something we can just turn a dial and make it lower. There WILL be a change order if we have to put an isolation transformer in for an elevator..

 

[jim dungar]

It's in the contractors' interest to get us the data (or the power study submittal) early on.

I have sat in meetings with electrical contractors owners were trying to get our company to pay for the SCCR fiasco and overruns. During the discussion it was pointed out the EC project manager never provided installed equipment data sheets and conductor data to the power study engineer. They never told us about all of the value engineering and changes they had implemented. This is why EC firms are usually not allowed to do these studies in house, on large projects.