Fuses and circuit breakers

yrtrnc · May 2013

Hi

Can someone pls point me in the right direction.

I have 3 of these babies below connected as a three phase setup. Can someone pls tell me what sort of fuses and circuit breakers I should use and where I could get em from online. They are connected to the batteries by 2 sets of 70mm cable (2 minus, 2 plus ) at around 4 Meters. Thanks in advance.

Specifications:

Inverter:
Input voltage range: 38V - 66V
Output voltage: 230V AC ±2%
Output frequency: 50Hz ±0.1%
Cont. output power at 25°C (non-linear load, crest factor 3:1): 10000VA
Cont. output power at 25°C: 9000W
Cont. output power at 40°C: 8000W
Peak power: 20,000W
Max. efficiency: 96%
Zero-load power: 35W
Zero-load power in AES mode: 30W
Zero-load power in Search mode: 10W

Charger:
Charge voltage – absorption: 56.7V
Charge voltage - float: 55.2V
Storage mode: 52.8V
Charge current house battery: 140A

General:
Auxiliary output: 50A
AC Input voltage range: 187 - 265V AC
AC Input frequency range: 45 – 65Hz
Maximum feed through current: 2 x 100A
Operating temperature range: -40 to +50°C (fan assisted cooling)
Humidity: Max. 95% (non-condensing)
Battery connection: Four M8 bolts (2 plus and 2 minus connections)
230V AC connection: Bolts M6
Weight: 45kg
Dimensions: 470mm x 350mm x 280mm

For full datasheet please go to:
http://http://www.victronenergy.com/upload/documents/Datasheet

BB. · May 2013

Re: Fuses and circuit breakers

I gues you are out of the Netherlands--So anyone that can help you with regional sources would be helpful.

The basics---What is your planned output power. The 25C rating is 9 kW and 38 volts minimunm (I would suggest ~44-46 volts - voltage drop as the minimum voltage--38 VDC is pretty low for a "48 volt" battery bank and wiring--plus it increases the DC input current with such low input voltage).

9,000 watts * 1/0.85 typical inverter eff * 1/44 volts min DC voltage = 241 amps DC

In the US, our NEC requires a 0.8 (or 1/0.80=1.25) derating factor for wiring and breakers. So, the DC branch circuit would be rated to:

241 Amps * 1.25 NEC derating = 377 amp branch circuit minimum

If you use a fuse (and cut off switch), these types are very nice:

http://www.solar-electric.com/infubr.html

Schneider does make large DC Thermal Breakers:

http://search.schneider-electric.us/search?q=dc+thermal+breakers&filter=0&output=xml_no_dtd&proxystylesheet=xhtml&client=xhtml&site=default_collection

But I hate to think how much those cost... As well as the copper cabling. This is not a small system and you might need to get a power engineer/system designer involved.

Does your local inverter supplier have any suggestions for wiring/breakers/etc... for your system?

-Bill

yrtrnc · May 2013

Re: Fuses and circuit breakers

Wow, thanks for all your info.

Actually Im in Cyprus and we dont have much regulation or knowledge here at the moment.

So, If I am using two 50mm wires for plus and minus for each inverter I should put two 200amp fuses on the plus side for each inverter right?

How about a cut off switch , so if I wanted to cutt off the power from the batteries to the inverter? What should I use ? Is a AC cutt off the same as a DC cutt off?

BB. wrote: »

I gues you are out of the Netherlands--So anyone that can help you with regional sources would be helpful.

The basics---What is your planned output power. The 25C rating is 9 kW and 38 volts minimunm (I would suggest ~44-46 volts - voltage drop as the minimum voltage--38 VDC is pretty low for a "48 volt" battery bank and wiring--plus it increases the DC input current with such low input voltage).

9,000 watts * 1/0.85 typical inverter eff * 1/44 volts min DC voltage = 241 amps DC

In the US, our NEC requires a 0.8 (or 1/0.80=1.25) derating factor for wiring and breakers. So, the DC branch circuit would be rated to:

241 Amps * 1.25 NEC derating = 377 amp branch circuit minimum

If you use a fuse (and cut off switch), these types are very nice:

http://www.solar-electric.com/infubr.html

Schneider does make large DC Thermal Breakers:

http://search.schneider-electric.us/search?q=dc+thermal+breakers&filter=0&output=xml_no_dtd&proxystylesheet=xhtml&client=xhtml&site=default_collection

But I hate to think how much those cost... As well as the copper cabling. This is not a small system and you might need to get a power engineer/system designer involved.

Does your local inverter supplier have any suggestions for wiring/breakers/etc... for your system?

-Bill

BB. · May 2013

Re: Fuses and circuit breakers

I forgot--It was Cyprus for you.

Anyway, I am not familiar with how Europe rates their metric wiring and insulation... For example, here is how they do it in large ships:

http://www.veristar.com/bvrules/C_2_s3_9_9.htm

You can try 200 amp fuses, one for each parallel + cable run... But in the US, NEC would have just used one fuse for the parallel cables (your way is safer).

How close to the 9kW rating do you plan on operating? And have you calculated the voltage drop for your 4 meter cable run (remember, it is 8 meters total round trip cabling--However, many cable drop calculators only need the one-way trip). Also, remember that you need to not have too much voltage drop during surge current periods (starting a well pump, etc.)--A good AC inverter can supply 2x rated watts during short term surge operation (a few seconds) and that current has to come from the battery bank (via the power cables).

Make sure you have spare fuses--You don't want to be left in the dark if you pop a fuse.

And DC switching is much more "difficult" vs AC switching. DC current tends to maintain arcs very nicely (DC Arc Welders are also much nicer to use vs AC).

So--If you can, you should find a DC rated disconnect (>250 amps @ 60 VDC).

And, if you think you will need a "panic" switch for the loads--You could put in an AC disconnect rated >40 amps @ 230 VAC -- A much smaller/cheaper/easier to find disconnect switch.

You could still use a >250 Amp AC rated disconnect on the DC side--But I would only switch it after the AC loads are turned off (and/or inverter shut down). That way, you will not have very much DC current to switch--It will be easier on the switch blades.

-Bill

yrtrnc · May 2013

Re: Fuses and circuit breakers

Thanks Bill.. Pretty neat info!

I doubt I will be able to find dc disconnects locally. The island is new to all this sort of stuff. A mate of mine fits car stereos and he said he has 200 amp fuses he could give me. I said they are 12v and probably wont work on my 48v system but he reckons they should be ok. What do you think Bill?

And you are right about the inverters, they can pump out 20KW for a few secs if need be. We will probably use half of the inverters rated value at the most, so 5KW per phase max.

We are using two 75mm flex cables for each pole per inverter. I just didnt know what kind of fuses and breakers to use and got a bit worried as we already fried one of the inverters before, which had no fuse :roll:.

Some one also suggested an AC HRC fuse with disconnect ?

BB. wrote: »

I forgot--It was Cyrus for you.

Anyway, I am not familiar with how Europe rates their metric wiring and insulation... For example, here is how they do it in large ships:

http://www.veristar.com/bvrules/C_2_s3_9_9.htm

You can try 200 amp fuses, one for each parallel + cable run... But in the US, NEC would have just used one fuse for the parallel cables (your way is safer).

How close to the 9kW rating do you plan on operating? And have you calculated the voltage drop for your 4 meter cable run (remember, it is 8 meters total round trip cabling--However, many cable drop calculators only need the one-way trip). Also, remember that you need to not have too much voltage drop during surge current periods (starting a well pump, etc.)--A good AC inverter can supply 2x rated watts during short term surge operation (a few seconds) and that current has to come from the battery bank (via the power cables).

Make sure you have spare fuses--You don't want to be left in the dark if you pop a fuse.

And DC switching is much more "difficult" vs AC switching. DC current tends to maintain arcs very nicely (DC Arc Welders are also much nicer to use vs AC).

So--If you can, you should find a DC rated disconnect (>250 amps @ 60 VDC).

And, if you think you will need a "panic" switch for the loads--You could put in an AC disconnect rated >40 amps @ 230 VAC -- A much smaller/cheaper/easier to find disconnect switch.

You could still use a >250 Amp AC rated disconnect on the DC side--But I would only switch it after the AC loads are turned off (and/or inverter shut down). That way, you will not have very much DC current to switch--It will be easier on the switch blades.

-Bill

yrtrnc · May 2013

Re: Fuses and circuit breakers

I think .75mm wire in USA is 21

niel · May 2013

Re: Fuses and circuit breakers

odds are the fuses he has are rated for higher than 12v, but you must determine if the rating is up as high as 48v for if it isn't the fuses could fail on you.

yrtrnc · May 2013

Re: Fuses and circuit breakers

Thanks for the reply!

Whats the best way to determine that the rated voltage is high enough? And what is high enough?

niel wrote: »

odds are the fuses he has are rated for higher than 12v, but you must determine if the rating is up as high as 48v for if it isn't the fuses could fail on you.

niel · May 2013

Re: Fuses and circuit breakers

usually the rating is stamped onto the fuse.

BB. · May 2013

Re: Fuses and circuit breakers

yrtrnc wrote: »

I think .75mm wire in USA is 21

We have to be very careful here... Are you typing about Diameter or mm². Are not most European companies using mm² for their specifications?

AWG specifications are more based on Area...

Double diameter, you get 4x the area and about 4x current capacity.
Double the area, you get ~2x current capacity
Going "down" 3 AWG is ~2x larger area, and you get ~2x current capacity.

So, I would guess you are looking at ~75 mm² wire which is between our 3/O and 2/O wire size. 3/O (85 mm²) is rated for around 165-225 Amps (depending on insulation, conduit fill, and ambient temperatures, using copper).

21 awg wire is pretty fine (maybe 5-10 amps of maximum current capacity). Our home wiring is nominally 14 awg (15 amp rated) or 12 awg (20 amp):

http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_awg_to_metric

[TH]AWG Number[/TH]
[TH]Ø [Inch][/TH]
[TH]Ø [mm][/TH]
[TH]Ø [mm²][/TH]

6/0 = 000000
0.580
14.73
170.30

5/0 = 00000
0.517
13.12
135.10

4/0 = 0000
0.460
11.7
107

3/0 = 000
0.410
10.4
85.0

2/0 = 00
0.365
9.26
67.4

1/0 = 0
0.325
8.25
53.5

1
0.289
7.35
42.4

2
0.258
6.54
33.6

3
0.229
5.83
26.7

4
0.204
5.19
21.1

5
0.182
4.62
16.8

6
0.162
4.11
13.3

7
0.144
3.66
10.5

8
0.128
3.26
8.36

9
0.114
2.91
6.63

10
0.102
2.59
5.26

11
0.0907
2.30
4.17

12
0.0808
2.05
3.31

13
0.0720
1.83
2.62

14
0.0641
1.63
2.08

15
0.0571
1.45
1.65

16
0.0508
1.29
1.31

17
0.0453
1.15
1.04

18
0.0403
1.02
0.823

19
0.0359
0.912
0.653

20
0.0320
0.812
0.518

21
0.0285
0.723
0.410

22
0.0253
0.644
0.326

23
0.0226
0.573
0.258

24
0.0201
0.511
0.205

25
0.0179
0.455
0.162

26
0.0159
0.405
0.129

27
0.0142
0.361
0.102

28
0.0126
0.321
0.0810

29
0.0113
0.286
0.0642

30
0.0100
0.255
0.0509

About the large AWG wire you will find in normal wiring situations (US) is probably 4/O. That is not thin stuff.

-Bill

BB. · May 2013

Re: Fuses and circuit breakers

Our host (NAWS in Arizona) has DC rated fuses like these:

And one of our posters here nigtomdaw has a web shop out of Spain--He can probably give you some guidance (if not parts) that are European based and spec'ed (you probably don't want to mix US and Metric fuse/mounting hardware together):

http://prismsolar.co.uk/shop/

http://www.solar-electric.com/infubr.html
http://www.solar-electric.com/pvaranddcrab.html

If at all possible, I would try to get "rated" fuses or breakers for the application. These are your last line of defense against fire. And fuses/breaker with too small of rating (voltage or amp interrupt current), are just about useless--They simply become the point of origin for the fire.

Just to give you an idea--In engineering terms, things that are within ~2x of each other, are about the same. Things that are 10x different, the smaller "thing" can be ignored.

So, if you have a 12 volt breaker on a 48 volt circuit--Not a good thing (4x difference). If you have a 48 volt breaker on a 48 volt battery bank (which can hit 60 volts during charging) is probably OK (less than 2x difference).

Obviously, such a rule of thumb does not fly with "code guys"--But for an area that does not have code enforcement, it gives you an idea what what will work or not.

Finding AIC (Amp Interrupt Current) is not obvious, and it can take a bit of web searching to find those ratings.

General Purpose Fuses JLLN/JLLS POWR-T™ Class T Fuses

Voltage Ratings:
AC: 300 Volts (JLLN); 600 Volts (JLLS)

DC: 125 Volts (JLLN 1 – 30A)

160 Volts (JLLN 35 – 60A)
125 Volts (JLLN 110 – 1200A)
300 Volts (JLLS)

Interrupting Ratings:
AC: 200,000 amperes rms symmetrical

DC: 20,000 amperes

(JLLN 110 – 1200A)
(JLLS 1 – 1200A)

See the difference between the AC vs DC voltage interrupt rating. And that for DC voltage, different size rated fuses have different interrupt voltage ratings.

Notice the AC AIC rating is 10x that for DC current.

This safety stuff is not obvious. I am no expert and I still cannot figure out some aspects of the ratings (what is "apparent symmetrical current rating" for AC?).

Having a "big" AC rated spring loaded knife switch on a DC Circuit for emergency cutoff (rated to carry the current, but no known DC interrupt listing)--You may get a nasty arc which damages the blades but it will still turn off the power--It just won't do that very often before you need to replace the switch. And for turning off power for maintenance on an inverter (with the inverter already shut down, or very light AC loads), it will probably work very nicely.

Most house type disconnects are rated for 600-1,000 VAC (US-Europe?)... Which is 10x your 60 VDC rated battery bank voltage. And rated for 10,000-200,000 AIC... So we are looking at 10x the AC rated numbers vs your DC system ratings... Again that 10x difference between the two--So, I would not be real concerned if I needed a DC switch for my system.

Things to avoid are switches that do not have "snap action" or slow turning handles (old manual knife switches, or some marine battery switches). These should not be switched under heavy loads (or with a short circuit) because you "pull" the contacts apart relatively slowly and that causes arcs to be started and sustained:

Manual knife switches:

Attachment not found.

I don't think this has a "snap action" and should not be switched under load, if possible:

Attachment not found.

I hope this helps. It is difficult to make things "safe" unless you understand that reasons behind the decisions.

-Bill

Fuses and circuit breakers

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