# 800a Mdp



## [email protected]&R (Jul 26, 2005)

Ok I have a 800A 120/208V 3P4W 10KAIC MDP to install. The prints are telling me I need 6- 3 1/2" conduits with 4- 500MCM in each conduit. Thats a total of 24- 500MCM to go into this panel. Each conduit is 200' long. That is a total of 4800 feet of 500MCM at $8.33 this is $39,984.00 + Tax. Hell im not even sure where to put all the wire. By my calculations I should only need 3- conduits with 4- 500MCM in each one. I think even 3- conduits with 4- 350MCM in each would deliver the 800A required.

Ok where am I going wrong here? I either have prints by a crackhead electrical engineer or I am missing something. The best part is I tried to contact the engineer and he is no longer in business. Hell this is only to power a restraunt and it's just an addition at that.


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## [email protected]&R (Jul 26, 2005)

Ok I went and bought a neat and niftey electrical calculator. It is telling me I can use 4- 4/0 THHN per phase. Sounds a litttle better then the jumble of 500MCM that was spected by the electrical engineer. Any opinions would be greatly appreciated. BTW all the calculations for both posts are derated by 80%.


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## acrwc10 (Dec 10, 2006)

This is off south wires voltage calculator. :thumbup: 



2 conductor(s) per phase utilizing a 600 kcmil Copper conductor will limit the voltage drop to 2.51% or less when supplying 800 amps for 200 feet on a 208 volt system.

For Engineering Information:

420 Amps Rated ampacity of selected conductor
0.023 Ohms Resistance (Ohms per 1000 feet)
0.039 Ohms Reactance (Ohms per 1000 feet)
6.24 volts maximum allowable voltage drop at 3%
2.51 Actual voltage drop loss for each cable at 2.51%
10.45 volts Total maximum allowable parallel voltage drop loss for the circuit
0.9 Power Factor


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## acrwc10 (Dec 10, 2006)

I would question the engineer on this, and offer a more cost effective option to the owner/builder. I agree that 4/0 is the way to go, You could even go to aluminum for a HUGE cost savings, I don't think the 80% rating is nessary it is doubtful they are going to run an 800amp continuous load. You can most likely derate the neutral quite abit also.If you do the job by what is needed and not what is spected,if aproved by owner, you could most likely do the job for the cost of the wire as speced in the first place.


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## [email protected]&R (Jul 26, 2005)

That is exactly what I was thinking. I used the $299 vision infosoft calculator and it came up with using 3- 3 1/2" conduits and 4- 300 MCM for each phase. That cut's the wire not only by 4 runs but also by 1/2 the price. Besat price I have for 500 is $6.18 and 300MCM is $3.89 per foot. That is a huge differance when buying 3000 - 5000 feet.


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## Sparky Joe (Apr 29, 2006)

We did a 400amp panel not long ago that was 600 feet from the MDP, we pulled 2 4/0s(instead of 3/0's because of the distance). We also used 2" PVC, but I wouldn't reccomend it without a tugger.

3" and 4 4/0's should do fine


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## [email protected]&R (Jul 26, 2005)

The EC the started before the whole team got booted already has 4- 3 1/2" SCH40 installed. I am going to meet with the owner of the building and the AHJ in the morning. I already have the owners permission to value engineer the building as I see fit as long as it passes inspection. The program im using says it's a no go with 4/0. So I am going to run three 300MCm per phase past the inspector and see what happens.


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## Sparky Joe (Apr 29, 2006)

By what I figure the 300's put you at a 1% voltage drop and you're allowed 3%, so I'm sure the inspector should have no problem.


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## mdshunk (Mar 13, 2005)

When I figure parallel conductors, I generally start with a quote from the supply house for 1 foot of copper THHN for every gauge from 2/0 through 600MCM. I divide that out, and figure out a cost per circular mil for each gauge I was quoted. That will let me know which gauge is cheapest at the moment. Then, I figure my parallel conductors based upon that gauge. It makes little difference whether you parallel a few 600's or a lot of 3/0's in the end. You just need develop some combination that will carry the load, 800 amp in this case. To do that economically, you need to know which gauge will do that for you most economically, and work from that. 

It would be helpful to know if these are service conductors or feeder conductors in this case, though. Makes some difference.


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## Sparky Joe (Apr 29, 2006)

Also consider the man hours of landing 500's compared to 3/0's, and of course the added or special lugs would counter act that. And also that 3/0 is 1/3 the size of 500, your pipe size goes down by 1/2, and I don't know the price difference. And also I pointed out in another post due to cmil difference this may lower your ground size too.

In all lots of things to figure, but I know I'd rather pull and deal with 3/0 over 500's any day of the week


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## [email protected]&R (Jul 26, 2005)

My main concern was the AHJ I know some areas have rules others do not. I got a bit pissed when I tried for a week to reach the inspector. I ended up calling his boss who is over all the inspectors in East TN. I got my anwsers and managed to not leave my name or company name so the local inspector can't take it out later. This plan of running 24- 500MCM for a 800A service seemed like major overkill. I have 2 choices given me from the head honcho. I can run 2- 500MCM per phase with same size neutral of course or I can run 3-350MCM per phase and same for neutral. It will run less then $600 between the 2 options. I think im going to loose the $600 and go with the 350 option. Easier to work with but the same amount of time to install it.

BTW they are service conductors.


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## Sparky Joe (Apr 29, 2006)

Don't mean to sound like a pain, but instaead of saying 24 runs, it's really just 6 runs, every electrician knows A,B,C phases and Neutral.

Nice sticking it to the inspector, but at the same time 'good luck', you know no on in that office talks to each other, then what? you tell him "I talked to your boss and he said.....", then he talks to his boss and ......"fail".

I think 4/0's will do it, and if he argues with 300's then you have a major problem pain in the ass inspector.


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## acrwc10 (Dec 10, 2006)

[email protected]&R said:


> Ok I have a 800A 120/208V 3P4W 10KAIC MDP to install. The prints are telling me I need 6- 3 1/2" conduits with 4- 500MCM in each conduit.
> Each conduit is 200' long.
> I either have prints by a crackhead electrical engineer or I am missing something.
> The best part is I tried to contact the engineer and he is no longer in business.
> ...


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## [email protected]&R (Jul 26, 2005)

acrwc10 said:


> [email protected]&R said:
> 
> 
> > Ok I have a 800A 120/208V 3P4W 10KAIC MDP to install. The prints are telling me I need 6- 3 1/2" conduits with 4- 500MCM in each conduit.
> ...


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## Sparky Joe (Apr 29, 2006)

[email protected]&R said:


> acrwc10 said:
> 
> 
> > He speced copper and after we went to see the place and talked to the owner about what he wanted built later we still cut it back to the 3 runs of 350. Right now it will only be pulling 330A and later he wants to build another same size addition to the other side. That sill only equals 660A hell by then the only thing he could do is build up and he wont be doing that.
> ...


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## [email protected]&R (Jul 26, 2005)

Sparky Joe said:


> [email protected]&R said:
> 
> 
> > That's typically why feeders will be oversized; for foreseen additions, and is a good call while the trenches are dug and everything is easy. Although usually the challenge is simply met by putting more conduits in the ground so more wire can be pulled as needed. Hell right now chances are copper prices will go down.
> ...


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## [email protected]&R (Jul 26, 2005)

BTW I hope no one see's this as some back stabbing way to get a contract by low balling. I just couldnt bring my self to intentionaly rip someone off of what could have been $10,000 - $20,000. Just because im the only one that mentioned it im sure some of the other bidders seen it and was just deciding to either pocket the extra completly (which is what it looks like since they only ran 3 out of the 6 3 1/2" conduits) or was going to pocket thier mark up for the extra $2,000 or $3,000. To me the satisfaction of having someone say you need electric use K&R they are honest people is better then the 2-3K or even the 10-20K. Who know's maybe we will even get a free steak dinner.


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## acrwc10 (Dec 10, 2006)

There is no better advertisement then being good and fair. :thumbup: 

I agree with sparky Joe about extra conduits in the trench. What you could do is run it at 400amp if the load is only 320 or so but put in a larger switch gear and extra conduit. Downsize the main breaker. Then if they want to add on later pull the wire then and change the main breaker out. Nothing wrong with an 800 amp panel with a 400 amp main. But I don't want to get you to down sized here. You might wind up paying to do the job if we give you to many cost cutting ideas.:laughing:


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## Sparky Joe (Apr 29, 2006)

[email protected]&R said:


> BTW I hope no one see's this as some back stabbing way to get a contract by low balling. I just couldnt bring my self to intentionaly rip someone off of what could have been $10,000 - $20,000. Just because im the only one that mentioned it im sure some of the other bidders seen it and was just deciding to either pocket the extra completly (which is what it looks like since they only ran 3 out of the 6 3 1/2" conduits) or was going to pocket thier mark up for the extra $2,000 or $3,000. To me the satisfaction of having someone say you need electric use K&R they are honest people is better then the 2-3K or even the 10-20K. Who know's maybe we will even get a free steak dinner.


We built a "Golden Coral" and got a couple free dinners, woo-hoo, hog heaven I tell you  

But in all honesty, the wire they had spec'ed would handle over 2000 amps, and there's no way an 800 amp piece of gear would handle that kind of current, every cabinet has an amperage rating. So even if they decide to pull the extra wire to upsize later, it would cost another 30k or so just to change out the inadequate swith gear(plus the down time).

I haven't seen it for myself, but my teacher told us about an undersized enclosure(just a steel box that wasn't rated), where the sides had completed 'sucked' in due to the magnetic field from the fault current traveling through it. :blink: 

In fact we got dinged once by a sharp inspector for a 200 amp fire pump, we installed a 200a meter socket(because the fire pump was a seperate service), he had us install a giant 800a CT can due to the locked rotor current of the pump motor. He was right in the end, but we didn't see it. :notworthy


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## mdshunk (Mar 13, 2005)

Sparky Joe said:


> In fact we got dinged once by a sharp inspector for a 200 amp fire pump, we installed a 200a meter socket(because the fire pump was a seperate service), he had us install a giant 800a CT can due to the locked rotor current of the pump motor. He was right in the end, but we didn't see it. :notworthy


Fire pumps are a horse of another color. You purposely severely upsize the overcurrent protection, and use fireproof wiring methods. You basically want that fire pump to run under all conditions, and want the service to actually self destruct to be the only thing that will shut the fire pump down. Wiring fire pumps, and services for fire pumps, runs counter to everything an electrician is ever taught. If you keep in mind that the fire pump must run, no matter what happens, then the whole fire pump wiring theory becomes a little easier to understand.


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