Wire and Fuse Sizing

[john61ct]

Originally Posted by FlyingScot

Winch at full pull while the other person flushes all the s**t would exceed 200 amps

I could have a lot of amps flowing through the batteries. I'm adding 4x360 watts solar with plans to make water during sunny days.

So just size for the sum of the biggest loads **you choose** to run concurrently. The one universal rule, is round up.

After all, you can pause the watermaker if you need to run the windlass.

Or decide it's worth spending a few extra boat bucks and adding heavy copper ballast in order not to have to make such choices, up to you.

[rgleason]

Originally Posted by Stu Jackson

Diversity is NOT choosing a %. It DOES involve use patterns, which can be ENGINEERED.

I've done hundreds of computer centers with backup power and UPS.

The way to do it is to properly define design criteria and engineer to meet those goals.

It ain't a guess. Anyone who is requested to do it that way, in my book, is completely correct in refusing to answer.

You misrepresent and take out of context what I stated and you are nitpicking. I stated

"..no Nynex Engineer was willing to commit to a % for load diversity. Not a single engineer would put his head on the line, basically because of the chilled water IBM Mainframes that had to be supported. Everything was sized for 100% load and a 10 minute transfer period to Generators when we had many disk drives and other accessories in the building.

You can do this once you know your use patterns. Figure out minimum and maximum loads, being realistic. Add them up. Consider diversity. You can also get into details like when you do stuff, like try to keep big loads focused around when the engines are running. Don't be like those chicken, Nynex engineers that, only knew what they didn't know and weren't willing to try to figure it out."

Continuing....
NYNEX engineers refused to determine anticipated loads for their computer data center, requiring 100% Full Load capacity. The computer division would not figure out how many tape and disk drives were likely to be working, the company did look carefully at power use after our continued questioning, but in the end after building a full list of all equipment, HVAC loads, Building Loads, Computer Loads, etc, we and our engineers were instructed to use the full list of computer loads at 100% for the design, with no allowances for machinery that was often off or at part load.

If your computer guys have lost power, do you think they're going to be busy processing new jobs? No. They're going to be scrambling to complete on going jobs and shut-down the main frame, because they always feared the generators would fail, to start and sometimes they did fail the first attempt. Loads will decline during the 10 minute transition, and at the begining of the emergency, loads might have normally been at 50%-70% to begin with. Mainframe Computer Data centers generally were way oversized at the time I was involved.

What a waste.

[FlyingScot]

Originally Posted by Lake-Effect

Like what? Every owner will run their boat in a different way, and have different load combinations.


If your boat's electrics are currently working, why not run with that for a while and record your current draws at various points? You might even find that a total rewire isn't necessary.

Like with ABYC. They seem to have a strong opinion about all things electrical on boats.

I agree that each owner will run the boat differently. This is exactly the reason I thought there would be a rule or guideline. A rule which would make it safe for the vast majority of people to operate the boat.

I guess what the ABYC does call for makes the boat safe. Each operator will learn to deal with what's on board regarding fuses/breakers, or upgrade it.

I don't plan a complete rewire by any means. I have to wire in three 4v batteries for 'house' bank. This is where it all started.

[Lake-Effect]

Originally Posted by FlyingScot

Like with ABYC. They seem to have a strong opinion about all things electrical on boats.

I agree that each owner will run the boat differently. This is exactly the reason I thought there would be a rule or guideline. A rule which would make it safe for the vast majority of people to operate the boat.

I guess what the ABYC does call for makes the boat safe.

Going backwards: yes, the ABYC researches, proposes and maintains a set of voluntary standards for boat technologies. In the absence of other mandatory or voluntary standards for boats, the ABYC standards have become the de facto guidelines for boat builders and maintainers.

But as you know, there's no standard boat (or owner). So the best they can do there is to provide advice on how to go about adding up your boat's electrical loads.

More in the way of practical advice comes from some noted authors like Don Casey and Nigel Calder. I was going to recommend Nigel's book, but while looking for the link I also found this set of articles on DC system sizing.

So, there's no simple rule of thumb, but some good info is around for how to determine your unique requirements.

[Cheechako]

I'd make a list of the most likely higher loads which may run simultaneously. Refridge, auto pilot, Radar maybe etc. Motor starting loads spike at up to 3x the operating power also... You're right ... it's impossible to predict it all, but short term overloads are not an issue anyway.

[Stu Jackson]

rg, I wasn't trying to misinterpret you nor to nitpick. My comments remain valid for PART of what you originally wrote.


Your followup is illuminating and absolutely correct. In the real world, just as you describe, I could NEVER get the damn IT geeks to tell us what their loads were for use by the electrical engineering, who had their own built-in psychological and logical faults!!!


Since they would only talk past each other, I patiently explained to them that because the data & telephone servers were no longer hardwired, that it was the number of individual receptacles that were required at the base of each server rack!!! Simple, for that portion of the electrical distribution system, 'cuz any less "plugs" would not work. Then I went and measured actual draws of the IT stuff, compared it with nameplate, to figure upstream loads.


You're right, they overbuilt 'cuz they refused to think.


Thanks for the stroll down memory lane!

Originally Posted by rgleason

You misrepresent and take out of context what I stated and you are nitpicking. I stated

"..no Nynex Engineer was willing to commit to a % for load diversity. Not a single engineer would put his head on the line, basically because of the chilled water IBM Mainframes that had to be supported. Everything was sized for 100% load and a 10 minute transfer period to Generators when we had many disk drives and other accessories in the building.

You can do this once you know your use patterns. Figure out minimum and maximum loads, being realistic. Add them up. Consider diversity. You can also get into details like when you do stuff, like try to keep big loads focused around when the engines are running. Don't be like those chicken, Nynex engineers that, only knew what they didn't know and weren't willing to try to figure it out."

Continuing....
NYNEX engineers refused to determine anticipated loads for their computer data center, requiring 100% Full Load capacity. The computer division would not figure out how many tape and disk drives were likely to be working, the company did look carefully at power use after our continued questioning, but in the end after building a full list of all equipment, HVAC loads, Building Loads, Computer Loads, etc, we and our engineers were instructed to use the full list of computer loads at 100% for the design, with no allowances for machinery that was often off or at part load.

If your computer guys have lost power, do you think they're going to be busy processing new jobs? No. They're going to be scrambling to complete on going jobs and shut-down the main frame, because they always feared the generators would fail, to start and sometimes they did fail the first attempt. Loads will decline during the 10 minute transition, and at the begining of the emergency, loads might have normally been at 50%-70% to begin with. Mainframe Computer Data centers generally were way oversized at the time I was involved.

What a waste.

[rgleason]

Sorry Stu, for any misunderstanding.

Since they would only talk past each other, I patiently explained to them that because the data & telephone servers were no longer hardwired, that it was the number of individual receptacles that were required at the base of each server rack!!!

How true. As an Architect I did not have all the tools necessary to pull all these guys together in the way I would have liked as I was just asking questions and learning. The answers worked out by our engineers became pretty embarrassing for everyone, including us, and we had to wring out old building systems, controls and alarms with big change orders. We were moving from ESS to digital and chilled water mainframes and liebert units were the norm for facilities like the billing center for all of New England.

Later for MCI on the 44th floor of Prudential, we did the first digital switchgear I had seen with no cable racks from above, but using cables under a Tate access floor. Eventually the air flow got constrained because the of cable mess below. They would just disconnect rack equipment and leave the unused cables! They had 1600 pair and used microwave out to Needham in the era of deregulation.

What was your job?

[Stu Jackson]

>>What was your job?



rg,


I was a mech eng for an international engineering firm. Started in NYC, spent three years+ in Iran from 75-78, moved to their SF office then, bought them out in 90 and started my own firm in 1994 (just me). I got tired of trying to get "my" electrical engineers to write sequence of operations for fire alarm systems; they kept saying the fire marshal would tell them what to do during construction! Idiots.
So my work from 94 on was Integrated Systems (HVAC, elec, fire protection) all work was direct for owners: design management of engineers hired by the architects, design build work based on my own specifications, commissioning, peer review...most of the work was for data/telecon centers with complicated backup power and dry pipe sprinkler sytems some with gaseous FP.

I enjoyed those years free of the burden of working with people who refused to learn something new.


You're right, the change from Liebert and cooled IT equipment changed the game, but essentially the building support "solutions" remained very similar.

[rgleason]

Very interesting. We mostly used halon in the computer data and battery backup areas.

[FlyingScot]

Originally Posted by Lake-Effect

Going backwards: yes, the ABYC researches, proposes and maintains a set of voluntary standards for boat technologies. In the absence of other mandatory or voluntary standards for boats, the ABYC standards have become the de facto guidelines for boat builders and maintainers.

But as you know, there's no standard boat (or owner). So the best they can do there is to provide advice on how to go about adding up your boat's electrical loads.

More in the way of practical advice comes from some noted authors like Don Casey and Nigel Calder. I was going to recommend Nigel's book, but while looking for the link I also found this set of articles on DC system sizing.

So, there's no simple rule of thumb, but some good info is around for how to determine your unique requirements.

I have Nigel's book and need to read it again regarding load sizing.

I'll check out the link too. Thanks for your input.

[smac999]

it's all about design and knowledge. like below is one simple thing. simply where the alts connect. but it effects that wire hugely.

that's a battery and pos and neg bus bars if not clear. every wire and fuse leaving the bar would be correct that that max load.

the wire between the battery and bus will never actually see max load.

[rgleason]

Are ANL Fuses preferred over Terminal and Mega or AMG when wiring batteries, alternator, switches because they have slots and can be changed faster in a jamb?



I was considering Terminal Fuses & Holders directly to the battery to save space and simplify installation on the batteries, but perhaps that is not the best approach. Also I am limited in space in the height direction and the Terminal Fuse receivers and Terminal Fuse require additional height.

[john61ct]

Top designs for high capacity are Class T, MRBF style, and ANL fuses.

MRBF at the bank itself, just be careful not to put heavy stresses at battery posts, can crack the outer case if cabling weights are not well supported.

[Colin A]

ABYC has a load worksheet in E11 they size some loads for 100% duty for saftey and others less so. This information is published on the web in several spots so I think it's ok to share here. From E11 section 8



In column A of TABLE ,
Electrical Load Requirement Worksheet, list the current rating
(amps) of the loads that must be available for use on a continuous duty basis for normal operations;


In column B of TABLE ,
list the current rating (amps) of the remaining loads that are intermittent, and total these loads. Take 10% of the total load in column B, or the current draw of the largest item, whichever is greater, and add this value to the total from column A to establish the total electrical load



.

[rgleason]

Thanks for the information. I know that Terminal MRBF or ANL are acceptable. I was interested in the preferences between them.



I believe MRBF holders will add about 1" to the height of my batteries which is a critical dimension, and I think they are harder to change because you have to unscrew the entire bolt, whereas ANL have open slots so you just loosen them and slip them out. So aren't these preferred generally?