Revise power distribution with no as-builts or load data???

[daryl927]

A school district client has asked us to evaluate the power capacity and distribution in their HS and MS. Both schools have 480/277V switchboards as their main service entrance/disconnect, but are still utilizing large (2000A) sub-fed 208/120V switchboards for all distribution throughout the buildings (to 208V branch panels throughout). I assume voltage drop could be a concern, along with no spare breakers in most panels.

I'm proposing to re-distribute power throughout the buildings at 480V (from the 480V main switchboards), step down to 208V in local elec closets, and then install new 208V branch panels to re-feed all loads in the vicinity of those closets. However, we have no as-built documentation of the existing panels/distribution, so we don't know the calculated or actual load on any panel/switchboard in the buildings except the metered 480V main switchboard.

I've solicited proposals from local EC's to do 30-day metering on select panels to determine actual load on panels, but the prices are too high for this project. So now all we know is the MCB size or mains size in each branch panel. How can we properly group these panels, and size distribution panels (on both sides of the 480/208V transformers) to feed the grouped 208V branch panels, if we don't have any actual load data and metering them is cost prohibitive? If we just add up the amperages/ratings of the breakers/mains ratings, the sizes of our transformers and distribution panels will be outrageous (and we know current is additive like load is)?

Any advice or rules of thumb??? Thank you in advance.

 

[Fitzdrew516]

Read 220.87

 

[Cow]

I've solicited proposals from local EC's to do 30-day metering on select panels to determine actual load on panels, but the prices are too high for this project.

They want to switch the entire distribution system over to 480v, but can't find the funds to do the legwork necessary to determine the scope of work?

Good luck.

 

[gadfly56]

How did you jump from "evaluate" to "re-distribute" with no work in between? What's your justification? This is what the word "survey" is all about. You go in, and trace the feed from the very last panel all the way back to the head end for each and every panel and you measure the lengths of the conductors, not just "wing it". Now you create the one-line as-builts and evaluate from there. Otherwise, I'm with Cow; they'll pay you all that money on a hunch but won't pay to be sure? Wow!

 

[don_resqcapt19]

If I was a taxpayer in that school district, I would have very strong objections to changing the distribution voltage unless there was some very strong evidence that there is a serious problem with the current distribution system. Sure systems need to be upgraded as time goes by, but changing the distribution system is way more than an upgrade.

Exactly what problem does this proposed project need to solve?

 

[steve66]

The School probably wouldn't have asked for an evaluation if there wasn't a problem. If this is like most schools, it was probably built in the 50's or 60's (or earlier) and probably had a very limited need for electric power.

Now they probably want to add computer rooms with 30 desktops and AC, and they may want to add AC to other classrooms.

I'd suggest you do some legwork and look at all the existing panels, look at the schedules and ratings, and review the existing drawings (if they have any).

You can get a rough idea what is required for lights and receptacles by doing a square foot calculation, and adding for special loads like computer rooms, shops, etc.

Worst case I would assume the existing panels are completely loaded.

Lets face it - some of it will just have to be educated guesswork. Maybe you can add monitoring to the project to confirm loads once (and if ) an electrician is hired for the upgrade.

 

[petersonra]

My limited experience with government entities of all kinds is that they are often looking to come up with any projects whatsoever to justify the funds they want to have in future budgets so they can hand those projects off to their favorite contractors.

I just don't see doing something like this half assed is a good approach. Either do it right or don't do it.

 

[steve66]

I think you are all being kind of hard on a new member. Its not his decision how the School spends their (or should I say our) money.

He asked a basic question, and in return all he gets is flack for suggesting that he may consider an upgrade to the school's electrical system.

Nothing in the original post leads me to believe he is doing anything "half assed". If fact, since he posted the question at all leads me to believe he is trying to do the best he can. Many engineers would be more than happy to just oversize everything, collect their fee, and move on.

He could kill the project telling the School they don't have the info they need, and they will probably just hire someone else that will do a bigger hack job, or spend the money on something even stupider.

 

[Ingenieur]

I would
get a floor plan
locate all panels on it
then off hours switch the feeders to determine where each is fed from
during operating hours measure v at the feeder cb and the panel
measure the i for each

a basic riser or single line can be developed

you are describing possibly a multi-million $$$ project involving several campuses
spending 50k up front is a no brainer

I have 2 questions
isn't this work required to be bid/proposals solicited
why not have an engineering firm do a feasibilty study then develop a plan


winging it seems crazy

 

[daryl927]

Thank you steve66 for understanding my exact question and responding appropriately. I appreciate the thoughtful response.

I am not a new member, and this is the exact reason why most people never post, and why I tell my engineers not to read too much into what people say in these forums.

No one is 'winging' anything or doing anything 'half-assed'.

 

[iwire]

Thank you steve66 for understanding my exact question and responding appropriately. I appreciate the thoughtful response.

I am not a new member, and this is the exact reason why most people never post, and why I tell my engineers not to read too much into what people say in these forums.

No one is 'winging' anything or doing anything 'half-assed'.

Well can you explain how you are going to comply with article 220 of the NEC without knowing the existing load and without 'winging it'?:?

Seems impossible to me, but I am willing to learn new things.

Just because the forum does no give you the easy answer you are looking for that does not mean the posts here are not helpful.

 

[daryl927]

That was my question. How to comply with 220.87 without existing documentation and without metering/tracing EVERYTHING. It's my belief that there is no way to determine existing loads otherwise, but I was hoping someone has come across a similar situation (with a school project) and could provide some insight on what they did.

This is a very common problem with school work. The voters pass a referendum with a line item that says 'replace electrical distribution system'. I then inherent that 'scope of work' and try to make sense of it while actually attempting to do what is right for that building and District.

I could easily replace everything in kind, add spare breakers in each location, and call it a day. But I'd like to think I'm more responsible than that.

In any case, I'll figure it out.

 

[don_resqcapt19]

That was my question. How to comply with 220.87 without existing documentation and without metering/tracing EVERYTHING. It's my belief that there is no way to determine existing loads otherwise, but I was hoping someone has come across a similar situation (with a school project) and could provide some insight on what they did.

This is a very common problem with school work. The voters pass a referendum with a line item that says 'replace electrical dI istribution system'. I then inherent that 'scope of work' and try to make sense of it while actually attempting to do what is right for that building and District.

I could easily replace everything in kind, add spare breakers in each location, and call it a day. But I'd like to think I'm more responsible than that.

In any case, I'll figure it out.

You have two choices, you either do complete Article 220 load calculations or you use metering equipment for at least 30 days. If you are just looking at the service load, you can use the demand information over a 1 year period from the utility if that is available.

Another place to start would be information on breakers that have been tripping. If there is no history of breakers tripping, there are no serious overloads, assuming that the breakers are functional.

 

[iwire]

That was my question. How to comply with 220.87 without existing documentation and without metering/tracing EVERYTHING.

I don't believe there is a way to avoid metering everything.

You either need the documentation to do a full load calculation or you must go with 220.87.

Of course I may be bias as I install recording meters on future projects often.

 

[Strathead]

Thank you steve66 for understanding my exact question and responding appropriately. I appreciate the thoughtful response.

I am not a new member, and this is the exact reason why most people never post, and why I tell my engineers not to read too much into what people say in these forums.

No one is 'winging' anything or doing anything 'half-assed'.

I could be wrong, but it is unlikely the people posting were stating you had an intention of doing anything half-assed. As I see it, it is standard operating procedure for and Engineer to "wing it". You get copies of the panel schedules, spend some time looking around for any loads or additional panels that jump out at you and then do a quick load calculation based on experience, square feet, the equipment you see, and a fudge factor that makes sure you aren't low. If that doesn't make you and the customer comfortable then the cost of an energy survey is what is costs. The meters cost almost $5,000 with CT's included, a laptop not included in this is another $1,000. And it takes about 1.5 hours at every panel to hook up and remove the CT's when you include the Class II suit. That is still going to be cheaper than tracing every single load. If the school district is smart, they will just go ahead and pay for an arc flash study to run concurrent. It is just too bad if the school board doesn't like it. That is what the rest of the government has decided all of us private businesses have to do. It isn't our fault or yours the school has done things over the years without proper documentation. One thing I find shocking is that the tax payers authorized a bond for such a vague request.

 

[iwire]

, it is standard operating procedure for and Engineer to "wing it". You get copies of the panel schedules, spend some time looking around for any loads or additional panels that jump out at you and then do a quick load calculation based on experience, square feet, the equipment you see, and a fudge factor that makes sure you aren't low. If that doesn't make you and the customer comfortable then the cost of an energy survey is what is costs.

Comfortable or not that is not compliant.

The meters cost almost $5,000 with CT's included, a laptop not included in this is another $1,000. And it takes about 1.5 hours at every panel to hook up and remove the CT's when you include the Class II suit.

Pretty spot on, we just ordered another recording meter and that is right in the ball park.

The one we own now was closer to $15K with accessories 15 years ago, but it does a lot more than just power.

 

[Strathead]

Comfortable or not that is not compliant.

It may not be compliant, but I am pretty sure that most Engineers across the country do it this way when they are doing upgrades to a building. I have lived in three different geographical areas, and it is pretty apparent to me that that is the way it is usually done.