Fuses, Breakers, Amps, Max Load... Crossy!

[Naam]

-supply to my home is 3x15 (3x45)amps

-wiring diameter from meter to home 3x10.6mm

(diameter not mm² of copper coil without insulation)

-distance meter to breaker box 16m (actual supply cable length)

-custom built "thingy" which switches off individual phase when voltage differs ±10%

-"thingy's" fuses per phase 32amps

-under certain conditions load exceeds 32amps on individual phases

(main reason number of aircons, total number withheld to prevent stupid and

irrelevant comments from the usual suspects)

-fuses are held in rail snap-in fuseholders (see below)

-to install stronger fuses (40amps) i have to change fuseholders too

question:

any objection for any reason to "upgrade" to 40amps?

[Crossy]

OK.

A 15/45 meter is quite happy fused at 40A (or with a 50A MCB) - Check.

Your incoming cable is pi * 5.3² = 88mm² (pretty enormous, was that an individual copper core you measured?) Is the cable actually marked with it's size? - Check (probably).

My only concern is the rating of the contactors (relays) in the 'thingy', the builders used 32A fuses for a reason.

Can you investigate the thingy and check the rating of the contactors (or post a decent photo of the internals so we can see for ourselves)?

Are you actually blowing fuses with your load? Often?

If you are having to replace the DIN mount fuse holders why not use MCBs? No more fuses to buy

[Naam]

thanks Crossy!

-cables are not marked, i measured before installation with a caliper. but i made a

mistake. just checked again, cable diameter is 8.6 = ~58mm² ! i insisted on a big

diameter because i requested 3x30amps and was told that will be actually 3x90amps.

little did i know that they will cheat me with 3x15

why not use MCBs? No more fuses to buy

-that would have been my next question!

-relays are S-N35 (found them in the net), rated 40amps

http://us.100y.com.tw/chanpin.asp?MNo=69393

-next to the porcelain fuses are 3 "Safe-T-Cuts" each 43amps

-i don't blow fuses often. it's just that i am principle beancounter and would like to have

the amps i have paid dearly for or at least the amps which my system can handle

[Naam]

so what's your verdict Crossy? relays rated for 40A means i can use 40A MCBs?

[Crossy]

Hi Naam, sorry been out on site earning a crust

It looks like the contactors have their contacts wired in parallel, so they're capable of 80A

Do the fuses feed in to the Safe-T-Cut devices (which appear to be 45A MCBs) which then feed the contactors? It's difficult to tell from the photo.

If the incoming supply does go through the fuses then the MCBs they will be the limiting factor, 40A (or even 50A) fuses would be appropriate. Using 50A fuses would ensure that the MCBs would open first in the event of an overload whilst retaining the 10kA breaking ability of the fuses in the event of a major failure, best of both worlds.

Nice to see you have surge arrestors (same ones as I have).

[doglover]

If you would open it up to the "general sparky populace" it would surely be more entertaining, and possibly even more informative. Even very skilled professionals can sometimes gain something from an apprentices enquiring mind.

[Crossy]

It's on the open forum, you're welcome to join in DL

[doglover]

I wasn't suggesting that I had any answers, but it looks more like an in/out relationship rather than parallel feeds to me.

[Naam]

Do the fuses feed in to the Safe-T-Cut devices (which appear to be 45A MCBs) which then feed the contactors?

no, fuses and safe-t-cuts (45A) are wired separately to the relays (contactors).

It looks like the contactors have their contacts wired in parallel...

??

so 40A MCBs are OK? if yes, what about their "behaviour"? in Germany we have

three different ones, called something like "fast", "moderate" and "lazy". i think it

indicates how many initial amps an MCB can take for a short time before tripping.

it's all about the bloody aircons with their high starting amps. if the "thingy" switches

off a phase totally because of a brownout then worst case scenario is that 7 aircons

switch on simultaneously when the voltage is back and the relay switches on automatically.

of course i could run to my "electric room" and switch off some of the aircon breakers.

but that applies only when i'm at home. for the Mrs and the maids even touching one

of the compartments is a big no-no.

of course all aircons are distributed evenly over the three phases!

[Naam]

I wasn't suggesting that I had any answers, but it looks more like an in/out relationship rather than parallel feeds to me.

that is not the case. even an apprentice like me can see that clearly (at the site, not from the picture!)

[Crossy]

40A MCBs will be fine, even 50A ones will be OK on your 15/45 meter. I'd go for 50A. Most MCBs available here seem to be 'C' curve (lazy) I'd stick with those with your A/C load.

Each contactor has two normally-open 40A contacts. These have been connected in parallel making a total contact rating of around 80A.

[Naam]

40A MCBs will be fine, even 50A ones will be OK on your 15/45 meter. I'd go for 50A. Most MCBs available here seem to be 'C' curve (lazy) I'd stick with those with your A/C load.

Each contactor has two normally-open 40A contacts. These have been connected in parallel making a total contact rating of around 80A.

-i hope i did not mess up with my parallel assumption.

let me explain again: contactor has below three what i would call "contacts"

-safe-t-cut is connected to left and fuse to the right contact (both with "shoe and screw").

middle contact is empty.

[Naam]

and now i see that i was somehow mistaken as there is a wire going from the arrestors to the contactors

edit: out of breath running back and forth i was right. wires from fuses and arrestors are connected (one on top of each other) with each contactor's right contact.

[Crossy]

I don't suppose you have a diagram?

The contacts appear to be linked at the top of the contactor, are they? and are they also linked at the bottom?

If the contacts are not linked at both ends then you should use 40A MCBs (in reality 45A or 50A would be just fine, contactors are very robust).

EDIT when I refer to 'contacts' I mean the actual switch inside the contactor, when 'on' they link the lower and upper connections on each.

The more I look at the photo the more confused I become.

Where in this device does your incoming supply arrive?

What is connected to the bottom of the fuses?

[Naam]

I don't suppose you have a diagram?

no, i don't.

The contacts appear to be linked at the top of the contactor, are they? and are they also linked at the bottom?

yes, left and right (what i call) contact is linked (bridged) on top with a wire. they are not linked at the bottom.

If the contacts are not linked at both ends then you should use 40A MCBs (in reality 45A or 50A would be just fine, contactors are very robust).

EDIT when I refer to 'contacts' I mean the actual switch inside the contactor, when 'on' they link the lower and upper connections on each.

now i am confused but try logical thinking. it looks like inside the contactor is a solenoid which links or cuts up from down.

The more I look at the photo the more confused I become.

Where in this device does your incoming supply arrive?

incoming supply from top going into a channel on the right side of the panel and from there up to MCB fuses (40A) and from there porcelain fuses (32A) (left). there's also one thick wire from down going to the arrestors. all three gadgets are connected to the three "timers/sensors" which show "on" as well as to three small relays located below.

What is connected to the bottom of the fuses?

"timers/sensors" says the apprentice.

[Naam]

let's call it a day Crossy. i'm tired running back and forth (each time ~60 meters),

need a break, a dip in the pool and a big glass of Port.

but thanks a lot for the time you devoted!

[Crossy]

What is connected to the bottom of the fuses?

"timers/sensors" says the apprentice.

If the fuses feed only the sensors, relays and contactor coils then upping their rating won't give you any more power.

I suspect that your actual power limiting devices are the Safe-T-Cut MCBs which are not opening so are not being overloaded.

One now wonders why you are getting 30A fuses fail when their load is minimal. Is it always one fuse? Are you sure they are actually 30A? Are you buying good quality fuses?

Replacing the fuses with MCBs may improve things anyway, so for convenience sake I would go with it. MCBs are cheap so I'd do a straight swap for similarly rated MCBs (go bigger not smaller if you can't get 32A).

[Naam]

-the fuses are 32A, have no idea as far as quality is concerned.

-the MCBs are 40A.

incidents:

-three times fuse blowing shutting off phase. once fuseholder melted and had to be replaced

caused twice by overload starting amps after a power cut and once by "slow" overload on the phase because of too many gadgets drawing power.

-several times MCB tripping shutting off phase caused by a specific short in the staff house.

the function of the sensors and the solenoid contactors i understand, but a layman like me wonders about the doubling of fuses and MCBs, different capacities, each able to shut down a phase.

does that make sense to you Crossy?

[Crossy]

Actually no

No issue with the short taking out the MCB, it's doing its job.

If the fuses feed only the sensors, relays and contactors how can a phase overload pop the fuse is my question?

The loss of a phase when the fuse opens is understandable as the sensor etc. will lose their power, but the overheating fuse carriers and popping fuses is a worrying mystery.

Can you mark up a photo identifying the incoming and outgoing supply cables please?

Still nothing to stop you replacing the fuses with MCBs of similar or slightly higher rating (40A).

[sandrabbit]

Naam, after reading your last post it suggests to me that you have a potential fire risk in that panel.

incidents:

-three times fuse blowing shutting off phase. once fuseholder melted and had to be replaced

caused twice by overload starting amps after a power cut and once by "slow" overload on the phase because of too many gadgets drawing power.

if fuse holders, fuses & wiring are correctly rated then there should be no significant overheating and if you have a fault don't keep resetting MCB's or replacing fuses. in industry I would be checking the security, i.e. tightness, of cable connections etc because if you have a bad connection then a high current consumption you will get a large voltage drop across that connection causing it to heat up. you should try to get somebody competent to trace out the circuit diagram and post it for us to check and also if you have had a number of faults and overloads then I would get someone to carry out an insulation check which is checking your resistance/reactance to ground.

I would replace all fuses with MCB's now as they are so cheap and provide a form of fire protection, if you look at the characteristics of MCB's (graph of current over time) if there is a fault current but not enough to trip it immediately the MCB will heat up and eventually it will trip thus preventing cables heating up and catching fire. I'm not trying to be a scaremonger, the pictures of the installation look good, but if you don't know what you're doing please get professional help as I've seen relays/contactors explode working in industry. My background is high power heavy industry so I'm never completely up to date on domestic installations so please check on current regulations/recommendations etc.

[Crossy]

Welcome to the mad world of Thai electrics sandrabbit

As an industrial sparky I would welcome your thoughts on the inrush current of contactor coils. Naam's panel has under-voltage sensors driving slave relays which in turn drive the contactor coils. It seems that the fuses are only feeding the sensors etc, the load current is not does not appear to be passing through them.

There is a problem with the 30A fuses popping, would you think that a single contactor coil is likely to pop a 30A fuse?

[khunPer]

»any objection for any reason to "upgrade" to 40amps?«

Your +/-10% devices are there to to protect your electronics for voltage deviations – an often used and good solution in Thailand. Looks like it has been installed correctly.

When upgrading fuses, you may need to check and eventually upgrade the cables, running from the fuses to the ourlets. If your cables are to small (thin), they will get warm or even hot – and can cause fire. 32A to 40A is +25%.

I am using the same kind of system to protect my electronics, but splitted with voltage detectors for each outgoing cirquit; as there may be areas you wish a higher protection for, like Aircons and waterpumps, and cirquits you don't need the same protection level, like light. The protection devices are not that costly, about 2,000 baht each set. Sometimes the selenoids (magnetic switches) do wear out and need to be replaced, but normally the shall last for many years.

[jackflash]

Hi Naam, Thanks for an interesting thread.

Nice to see some neat and tidy Electrical wiring in LOS for a change.

I agree that a wiring diagram would be an excellent idea. You really should have one posted on the inside of the cabinet for the Sparky.

I'm an Electronic Engineer, and although Electrical Diagrams are quite different to Electronic Circuit Drawings, I can probably figure one out.

Can't be much help without a diagram.

One Comment, you mentioned that multiple Airconditioners starting together will sometimes trip a Breaker.

Are you aware that there a Delayed Start Timers available to fix this very problem?

You wire one in series with each Air Con, and after a black-out they wait a random time to re-engage so that you don't get such a big spike of start-up current.

The destructive failure of the fuse assembly is definitely a worry. The only thing which should be able to do this is a nearby lightning strike,

or a 22KV line dropping onto the 240V lines after a traffic accident, etc.

Perhaps a big surge has caused the Spike Supressors to conduct, thus taking out the fuses catastropically, but the surge suppressors somehow survived

(assuming they are not now open-circuit).

[Naam]

Actually no

No issue with the short taking out the MCB, it's doing its job.

If the fuses feed only the sensors, relays and contactors how can a phase overload pop the fuse is my question?

The loss of a phase when the fuse opens is understandable as the sensor etc. will lose their power, but the overheating fuse carriers and popping fuses is a worrying mystery.

Can you mark up a photo identifying the incoming and outgoing supply cables please?

Still nothing to stop you replacing the fuses with MCBs of similar or slightly higher rating (40A).

my apprentice opinion is that the fuses and the MCBs are feeding the contactors and the outgoing supply comes from the contactors.

picture: the upper row cables right side "in", left side "out". the "in" cables are in an integrated channel on the right side, go all the way down and then through the varies thingies up again.

[Naam]

»any objection for any reason to "upgrade" to 40amps?«

Your +/-10% devices are there to to protect your electronics for voltage deviations – an often used and good solution in Thailand. Looks like it has been installed correctly.

When upgrading fuses, you may need to check and eventually upgrade the cables, running from the fuses to the ourlets. If your cables are to small (thin), they will get warm or even hot – and can cause fire. 32A to 40A is +25%.

I am using the same kind of system to protect my electronics, but splitted with voltage detectors for each outgoing cirquit; as there may be areas you wish a higher protection for, like Aircons and waterpumps, and cirquits you don't need the same protection level, like light. The protection devices are not that costly, about 2,000 baht each set. Sometimes the selenoids (magnetic switches) do wear out and need to be replaced, but normally the shall last for many years.

actually i installed the protection devices only to save on burned aircon and pump relays which i had to replace frequently in olden times due to brown-outs.

all our electronics are additionally protected by 3 inverters (not UPS toys but 320A each) which kick in when voltage deviates too much.

even though i am a "sparkie apprentice" i have a hard time not taking your advice of upgrading the cables to the outlets as a terrible insult. this time i will overlook the remark. next time expect my seconds to knock at your door and challenge you for a duel, "heavy sabres sine sine" on sunday morning at dawn in my front garden

[Naam]

Hi Naam, Thanks for an interesting thread.

Nice to see some neat and tidy Electrical wiring in LOS for a change.

I agree that a wiring diagram would be an excellent idea. You really should have one posted on the inside of the cabinet for the Sparky.

I'm an Electronic Engineer, and although Electrical Diagrams are quite different to Electronic Circuit Drawings, I can probably figure one out.

Can't be much help without a diagram.

One Comment, you mentioned that multiple Airconditioners starting together will sometimes trip a Breaker.

Are you aware that there a Delayed Start Timers available to fix this very problem?

You wire one in series with each Air Con, and after a black-out they wait a random time to re-engage so that you don't get such a big spike of start-up current.

The destructive failure of the fuse assembly is definitely a worry. The only thing which should be able to do this is a nearby lightning strike,

or a 22KV line dropping onto the 240V lines after a traffic accident, etc.

Perhaps a big surge has caused the Spike Supressors to conduct, thus taking out the fuses catastropically, but the surge suppressors somehow survived

(assuming they are not now open-circuit).

i'm aware that delayed start gadgets are available but the chance is extremely low that it will happen again.

[Mudcrab]

»any objection for any reason to "upgrade" to 40amps?«

Your +/-10% devices are there to to protect your electronics for voltage deviations – an often used and good solution in Thailand. Looks like it has been installed correctly.

When upgrading fuses, you may need to check and eventually upgrade the cables, running from the fuses to the ourlets. If your cables are to small (thin), they will get warm or even hot – and can cause fire. 32A to 40A is +25%.

I am using the same kind of system to protect my electronics, but splitted with voltage detectors for each outgoing cirquit; as there may be areas you wish a higher protection for, like Aircons and waterpumps, and cirquits you don't need the same protection level, like light. The protection devices are not that costly, about 2,000 baht each set. Sometimes the selenoids (magnetic switches) do wear out and need to be replaced, but normally the shall last for many years.

actually i installed the protection devices only to save on burned aircon and pump relays which i had to replace frequently in olden times due to brown-outs.

all our electronics are additionally protected by 3 inverters (not UPS toys but 320A each) which kick in when voltage deviates too much.

even though i am a "sparkie apprentice" i have a hard time not taking your advice of upgrading the cables to the outlets as a terrible insult. this time i will overlook the remark. next time expect my seconds to knock at your door and challenge you for a duel, "heavy sabres sine sine" on sunday morning at dawn in my front garden

320A inverters? You sure? Not 320 Watts? if they are 320A UPS then they will be very large.

[Mudcrab]

Hi Naam, Thanks for an interesting thread.

Nice to see some neat and tidy Electrical wiring in LOS for a change.

I agree that a wiring diagram would be an excellent idea. You really should have one posted on the inside of the cabinet for the Sparky.

I'm an Electronic Engineer, and although Electrical Diagrams are quite different to Electronic Circuit Drawings, I can probably figure one out.

Can't be much help without a diagram.

One Comment, you mentioned that multiple Airconditioners starting together will sometimes trip a Breaker.

Are you aware that there a Delayed Start Timers available to fix this very problem?

You wire one in series with each Air Con, and after a black-out they wait a random time to re-engage so that you don't get such a big spike of start-up current.

The destructive failure of the fuse assembly is definitely a worry. The only thing which should be able to do this is a nearby lightning strike,

or a 22KV line dropping onto the 240V lines after a traffic accident, etc.

Perhaps a big surge has caused the Spike Supressors to conduct, thus taking out the fuses catastropically, but the surge suppressors somehow survived

(assuming they are not now open-circuit).

i'm aware that delayed start gadgets are available but the chance is extremely low that it will happen again.

A surge suppressor (the term that has been used here) usually can (should) handle multiple voltage spikes before total failure. Each spike will degrade the internals until the end of the devices life. They should not fail on the first voltage spike. Are the neighbours experiencing similar issues...this could point to a supply authority issue. If not then you need to look closely at he actual wiring in your home, its hard to determine if the board is correctly wired from photos.

[Chao Lao Beach]

I am not suggesting doing this at all, I know nothing.

I also have 3X 15(45) ( 3 X single phases like Naam)

I was wondering hypothetically if it was 1 X 3 phase, would that offer more ooomfffff at peak air con start as it is "impossible" to share evenly the load over 3 circuits as you have to factor in things like hot water draw downs etc.

One more question, What is it called. It is a little sacrificial device on each cable on my side of the meter up high that is grounded. Something to do with a massive over voltage like a lighting strike on the lines out side of the property.

[Crossy]

picture: the upper row cables right side "in", left side "out". the "in" cables are in an integrated channel on the right side, go all the way down and then through the varies thingies up again.

Good Naam, where is the other end of the 'IN' cables, the MCBs perhaps?

Things are becoming clearer through the haze