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Posted By: scjohn 350 mcm for 300 amps? - 04/03/04 02:04 PM
I will be running my service (208v-3phase-300 amp) to an office building next week. The run is 100 ft. from poco transformer to meter base, and around 80 feet from meter to the 300 amp main. The engineer specs 350 mcm for the run. With copper going through the roof I cant see why I shouldnt be able to run 300 thhn. Total connected load is around 225, no electronics. I did a vd calc and 300 keeps me well within the 3%. Its a 4 wire system, but 310-15-4 states the neutral is not considered when it is used to carry the unbalance. Is there something obvious that I am missing? Thought I would ask, before I call the engineer.
Thanks, John
Posted By: Ryan_J Re: 350 mcm for 300 amps? - 04/03/04 04:18 PM
You should be fine. You could actually use 300KCMIL and use the round-up rule (240.4). You are right, the nuetral probably won't be a current carrying conductor, but even if it were you would be alright because for derating you can use the 90 degree column.

One thing, however: I notice that you talk about the connected load. 230.42 requires that you use the calculated load for the purpose of sizing service conductors. HAve you done a load calculation?
Posted By: golf junkie Re: 350 mcm for 300 amps? - 04/03/04 04:32 PM
"The engineer specs 350 mcm for the run. With copper going through the roof I cant see why I shouldnt be able to run 300 thhn."

Because the engineer spec'd 350 and you bid 350. In my experience if I was to ask to run the 300 two things might happen.

1) (mostly likely) the engineer would stick with his original decision for the 350.

2) (not as likely) They might accept the 300 and ask for a deduct.

On engineered jobs the service conductors are often oversized. The increase in coppper prices is not the engineers problem, it's your's.

GJ
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/03/04 06:34 PM
Golf Junkie, when I bidded this job 6 months ago 350 was actually a little lower than 300 is now. Its not like I am asking to substitute 12 gauge with 14 gauge, or install residential grade devices instead of commercial grade. What potential benefit is there in running 350 mcm as opposed to 300?
John
Posted By: electure Re: 350 mcm for 300 amps? - 04/03/04 07:24 PM
I think GJ's right.
The benefit is to you. You won't have to buy 350 over and above the price of the 300, pull out the 300, and do the job over with the 350

I don't know what you'd want to do with the 720' of 300kcm that had been pulled out, but I wouldn't want it sitting around the shop here.
Posted By: winnie Re: 350 mcm for 300 amps? - 04/03/04 08:54 PM
scjohn,

Do your bids have an expiration on them? If you bid for a particular job, then IMHO providing less than what you bid to provide is essentially stealing.

But the other side of the coin is that copper prices have gone through the roof, and you bid this job _6 months_ ago, and your underlying costs have gone up quite a bit.

IMHO it is _not_ immoral to take a bid off the table after a period of time. Have you now signed a contract based upon the bid and are starting work, only to get sticker shock on the cost of the wire, or is the customer asking you to start the job now, and you think that things should be renegotiated because of the delay?

-Jon
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/03/04 11:10 PM
We are in the final stage of the job. The service is one of the last things to do. I collected a rough draw 5 months ago. I dont know why it took so long for them to get us back in for trim. Someone stated in a previous post that eng. specs. usually go large on the service. Are they in bed with suppliers? Who is cheating who? This engineer also spec. bolt in panels, a $1200.00 surge suppressor, an aic rating of 24, which I talked him down to 22. A lighting package in excess $15,000 with low voltage lights galore all for a shell with cubicles. I spoke with the gc and the owner and we got the lighting down to $8000. I have basically helped the owner/gc every way possible to cut cost that was not within my bid, so I guess I neeed to go to them, instead of the engineer, and try to explain why they do not need a 350 mcm service so I do not lose profit on this job. I didnt mean for this thread to be morally oriented, but now that it has become such, I again ask is there a need for 350 mcm on a 300 amp service? Any engineers wish to reply??
Thanks, John
Posted By: caselec Re: 350 mcm for 300 amps? - 04/03/04 11:46 PM
John,

What happens at a later time if additional loads are added to this service and the calculated load is now at 286 amps? Who cheated who? If I was the owner and requested a 300 amp service I should get a 300 amp service not a 285 amp service. Most of projects I would on I am also the designer so I have the freedom to select the conductor sizes. The cost difference between the 300 and 350 can’t be a very high percentage of the total project. Since you bid the job with 350’s if you decide to use 300’s are you going to reduce your bill for this work accordingly?

Curt
Posted By: winnie Re: 350 mcm for 300 amps? - 04/03/04 11:54 PM
scjohn,

I have to apologize; it was inappropriate for me to moralize this discussion. We all take it as a given that doing less work, or installing smaller wire than is _agreed_ is not appropriate.

The real issue is: One of the promised materials is far in excess of what the customer needs. Materials prices have changed suddenly and unexpectedly, such that delivering the promised goods at the promised price means that you don't make your deserved profit.

There are two questions that this discussions can help answer: 1) Would installing smaller wire result in a safe and proper installation. 2) How can you pitch this change to the customer, so that they will agree to the change and both of you will come away from the deal reasonably satisfied.

The answer to 1) seems to be yes.

I wish I had better customer relations skills so that I could help you with 2)

I personally think that there are innumerable ways that one can 'oversize' in order to 'increase safety', which are not at all really necessary nor which actually increase safety. Engineers oversized things whenever they are not spending their own money! It has nothing to do with being in the pockets of suppliers, or trying to cheat anyone. It is simply 'bigger is better' combined with 'someone else's money'.

-Jon
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/03/04 11:56 PM
Caselec, 300 mcm is rated at 320 amps -310-16.With what your saying the engineer should have spec a 400 amp main with 500 mcm feeders. The main is what it is no more, no less.
John

[This message has been edited by scjohn (edited 04-03-2004).]
Posted By: caselec Re: 350 mcm for 300 amps? - 04/04/04 12:40 AM
John,

I have never seen 300 amp service equipment with 90C rated terminals. You need to use the 75C column for these conductors.

Curt
Posted By: Bjarney Re: 350 mcm for 300 amps? - 04/04/04 12:57 AM
If part of the run is underground, wouldn't the 75°C {THWN} rating likely apply?

Aside from that, 350-kcmil seems like part of the bid-process "level playing field." As being on the side of the specifier and his client, presupposing different calculations and ratings not specified could be viewed as shortchanging the building owner.
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/04/04 12:59 AM
Caslec, it is an underground service with thhn, not thwn.
John

[This message has been edited by scjohn (edited 04-03-2004).]
Posted By: caselec Re: 350 mcm for 300 amps? - 04/04/04 01:02 AM
John,

You can’t use the 90C rating if your terminals are only rated for 75C.

Curt
Posted By: resqcapt19 Re: 350 mcm for 300 amps? - 04/04/04 01:07 AM
John,
THHN is not suitable for use in wet locations. Underground raceways are wet locations.
Don
Posted By: caselec Re: 350 mcm for 300 amps? - 04/04/04 01:12 AM
I accidentally clicked post before I finished typing………

I will admit that all of the THHN I have seen is also rated as THWN but THWN is also only rated as a 75C conductor unless it’s THWN-2. You still can not use the 90C column if your terminals are only rated for 75C.

Curt
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/04/04 01:18 AM
OK CURT, than the 300 mcm will burn clear through before the 300 main will trip???
This thread is turning way away from its start. Please show me where 350 mcm is needed in this application, Curt!
John
Posted By: caselec Re: 350 mcm for 300 amps? - 04/04/04 01:35 AM
John

If the total load on this service is 225 amps you are correct 240.4(B) would permit the installation of 300 kcmil protected by a 300 amp breaker or fuse. If the calculated load on this service is >285 amps 350 kcmil cables would be required. If you signed a contract to install the electrical system according to the plans you need to follow them.

Curt
Posted By: winnie Re: 350 mcm for 300 amps? - 04/04/04 01:40 AM
Lots of posts on all aspects of this. I will try to summarize;

Using table 310.16:

350Kcmil Cu is rated for 260A if 60C insulation and terminations, 310A is 75C insulation and terminations, and 350A if 90C insulation and terminations.

For 300Kcmil, the values are 240A, 285A, and 320A.

(Assuming the ambient temperatures, etc...)

Most type THHN wire is dual rated as THWN. You can use whichever rating applies to the circumstances; eg. if the wire is in a wet location, then you cannot use the wire as THHN, but can use it as THWN. THWN wire is only rated at 75C insulation. If the wire is dual rated to THWN-2 then you can use it at 90C.

If you want to be able to use the 90C ampacity, then all of the terminations will also need to be rated for 90C.

If your wire is rated for 75C in wet locations, or if your terminations are rated for 75C, then you will need to use the 75C ampacity for the wire. This means 350 Kcmil to supply 300A.

However if the calculated load is <285A, then you could use 300 Kcmil wire protected with a 300A breaker.

Ryan, did I get the above correct?

-Jon
Posted By: winnie Re: 350 mcm for 300 amps? - 04/04/04 01:54 AM
Quote

If you signed a contract to install the electrical system according to the plans you need to follow them.

This is not quite true. It is true within the limits of contract law, but presuming that the contract is legal, and that the customer held up their end of the contract, then I believe that scjohn can reasonably _request_ a change.

If scjohn has treated the GC and customer well, then it is not in their interest to leave him screwed over because copper prices went through the roof. It is also not in their interest to pay him more or get less copper, so they will have to balance those issues, and scjohn will have to be persuasive.

But this should be a lesson to the rest of us; include in the fine print in your contracts reasonable 'escape' clauses. Bids should be of limited duration, and work should proceed at a reasonable pace. If the customer or another contractor delays the work (delays getting you paid), then your bid should accommodate changes in your costs.

What would happen if you started a job, then something happened to put it on hold for a couple of years...you've given people raises, copper and steel prices have changed, etc. What do your contracts say? Would you be left holding the bag?

scjohn was not paid up front, and the job waited six months from the bid and start of work (more or less; I don't know the exact timing). Why should he front out of pocket to buy the copper up front, if he has to wait months before he could install it and get paid. What would happen to _you_ in the same situation. Would you end up eating the price increase, or do you bid in a way that lets you pass the price increase on, yet still make a _fair_ profit?

-Jon
Posted By: nesparky Re: 350 mcm for 300 amps? - 04/04/04 02:18 PM
This thread has several on going issues with bids and contracting.
1) scjohn has an over engineered project for the service. This could change if the owner will accept a change order. The job was bid with the 350 for the service so any thing different would require a change order to put in place.
2) The job may have a scheduling problem. We don't know how long the job was supposed to take as planned. Have there been delays beyond normal construction lead times?
3) The one that is costing us all money the HUGE price increases for steel, copper, and gas. Maybe the owner will be receptave to an extra based on unexpected costs beyond your control, but I would not get my hopes up.
All these are part of what makes contracting a gamble.
Who need Las Vegas, you gamble every time you bid.
Posted By: Ryan_J Re: 350 mcm for 300 amps? - 04/04/04 02:54 PM
Quote
Ryan, did I get the above correct?

-Jon

Hi Jon (Winnie). It looks like you summed it up nicely. [Linked Image]

I think that there is a lot of misunderstanding on 310.16, especially when you throw 110.14 and 240.4 into it. The only thing that I would add is that I personally have never seen 90 degree terminations, and it is my understanding that these terminations are generally only found on power plant and high voltage types of installations.
Posted By: golf junkie Re: 350 mcm for 300 amps? - 04/04/04 03:24 PM
scJohn,

Please post back after you speak with the engineer. I'm curious what type of response you will get.

With the price increases we are seeing I believe that everyone who does contract work will be feeling the squeeze this year.

It sucks to win a job at a fair price, do everything right, and watch your margins evaporate due to circumstances beyond your control.

GJ

And good luck to you! Hopefully there will be some profit in this job.

[This message has been edited by golf junkie (edited 04-04-2004).]
Posted By: Nick Re: 350 mcm for 300 amps? - 04/04/04 05:01 PM
I would just add that the terminations and the enclosures have to be rated for 90 deg to use that ampacity.
Posted By: iwire Re: 350 mcm for 300 amps? - 04/04/04 08:53 PM
I thought Golf Junkie answered this perfectly.

Quote
1) (mostly likely) the engineer would stick with his original decision for the 350.

2) (not as likely) They might accept the 300 and ask for a deduct.

What am I missing, what other options are there.

Sorry if I sound harsh here, but what business is it of yours what size wire is specified?

The majority of jobs I work specify wires larger than necessary.

How about 350 Kcmils for 225 amp feeders less than 100' long?

We have done that, and we did not care why.

We install what we bid, or we ask for a change and get one of the results GJ has posted.

Bob
Posted By: wa2ise Re: 350 mcm for 300 amps? - 04/04/04 09:29 PM
Would aluminium wire sized to be the equivalent of 350 mcm copper be cheaper and acceptable to the customer?

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I'm having roast rabbit for Easter dinner [Linked Image]
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/04/04 11:11 PM
Iwire qouted:
--------------------------------------------
The majority of jobs I work specify wires larger than necessary.
--------------------------------------------

That is exactly what I have the problem with. And I also try to have a good working relationship with my clients. Yes I did bid this job for 350 mcm, I also had my supplier deal directly with the gc and owner on the lighting package without any % charge. I am an electrical contractor, not an engineer, but when I see where there might be a spec. that is beyond the need I will make it my BUISNESS to inform the owner/contractor, who else is going to. This is not just about the $300 extra I will pay for the 350. But also the money that was saved on the lighting package, and the main aic rating. I will call the engineer tommorow, again, and see what he has to say. If he allows me to run 300, I will offer to kick it back to the gc. What the heck, it will be an easier pull for my guys.
Thanks for all the replies, John
Posted By: iwire Re: 350 mcm for 300 amps? - 04/04/04 11:30 PM
When I said this.

Quote
The majority of jobs I work specify wires larger than necessary.

I should have made it clear I meant larger than required per code.

I still do not see why you care the reasons the wire is larger than code required.

If you signed a contract for a new truck with a 5.8 L engine would you want your mechanic telling you a 5.0 L is more than enough and it will be easer for us to give you a 5.0?

Sorry I just do not get it, maybe you should have brought it up as an alternate on your bid.

To each there own.

Good luck with whatever way you end up going.

Bob
Posted By: scjohn Re: 350 mcm for 300 amps? - 04/04/04 11:45 PM
Iwire, have you not read this entire tired thread? Why do I care?? I just hope one day you are on the other side. Lets say you go buy a truck for simple hauling, no major towing. The salesman tells you that you need to buy the truck with the 4.10 gear instead of 3.55's and a transmission cooler at an extra cost of $1500.00, you not knowing what he is talking about agrees.
John
Posted By: iwire Re: 350 mcm for 300 amps? - 04/05/04 12:28 AM
John I have read with the entire thread. [Linked Image]

I agree with almost all of the replies.

If you had an issue with the wire size you should have brought it up at the bid not now.

I just don't get it.

I wish you luck either way and I mean that, I do not want to see any EC lose money.

Bob
Posted By: electure Re: 350 mcm for 300 amps? - 04/05/04 01:28 AM
scjohn,
Our company is on the "other side of the fence" in a big way.
We've got 2 large auto dealerships going that bid early last summer. They started in September, and should be done by the end of this coming summer.
One has no steel conduit at all in yet, and neither has any copper in.
We'll not be "reengineering" the job in any way. It will go in as originally agreed.

I agree with iwire's last post 100% (gee, twice in the same day!)
Good luck
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