# Interest group forums > Electrical Contracting Industry Forum > Electrical Load Shedding Forum >  35A change over switch.

## Derlyn

Had to do a generator installation during the week so off I went in search of a change over switch.

At the one wholesaler they had 2 on offer, both MCE brand.
The one, 35A and the other 63A.

I enquired: Who buys a 35A change over switch ?
Answer:      The guys who install small generators.

I chuckled and explained to the young lad that when the generator is not in use, the total current drawn by the installation
is still going through the switch, which on a single phase domestic installation can be up to 60A.

It took me quite a while to convince him.

Wonder how many clients have underrated change over switches as a result of incorrect advice received, but more importantly,
it seems as if there are "sparkies" out there who also don't understand this because the same lad said " these 35A units are flying off the shelves".

I bought the 63A unit and left, shaking my head in disbelief.

In my opinion, MCE should not even make a 35A change over switch mounted in an enclosure and labelled eskom  ..  off  ..  generator.
Cannot think of an installation where it would work and not be underrated.   :Confused: 

Am I missing something ?

Peace out  ..  Derek

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## Justloadit

Maybe the 35A is "switching rating" not carrying current rating, but rather break and make current rating. 
Once a switch has closed, the current flow through it can be much higher, provided you do not open the switch.

In the case that it is used here, the chances that the switch will disconnect a heavy load is highly unlikely, and hence the reason they are getting away with.

Even so, there is a reason why one must read and understand "Specifications"

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## GCE

> In my opinion, MCE should not even make a 35A change over switch mounted in an enclosure and labelled eskom  ..  off  ..  generator.
> Cannot think of an installation where it would work and not be underrated.  
> 
> Am I missing something ?
> 
> Peace out  ..  Derek


Hi 

We would use the 35Amp switch , create an essential DB with protection of 25Amps whether we feed mains or generator to stay within the SANS 10142 code 7.12.2.4
In PE I don't believe you can use the 63Amp switch as the Municipal mains CB in the meter box is generally 80 amp and would not offer the protection as most domestic installations have isolators as a main switch.

We also use smaller change over switches on geyser element/heatpump installations and UPS installations - 

To me there is a need for smaller changeover switches 

To answer your question " Am I missing something " - yes you are  :Smile: 

_7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply
as a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded_

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## Justloadit

Provided of course that the full load from the municipality is not being switched through the change over switch, if the main supply is rated above the 35A.
In my case I have a 3 phase 80Amp mains supply, where the whole load is switched through the change over switch when the generator runs.

The original 80A change over from ACDC, Neutral contact burnt out when it was running off the municipal supply, and we replaced it with the 100A.

So it depends, if you are only using it to switch a partial load at the site, then the 35A may be more than adequate.

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## ians

> _7.12.2.4 Where the alternative supply is intended to provide a supply to an
> installation that is not connected to the main supply, or to provide a supply
> as a switched alternative to the main supply, the capacity and operating
> characteristics of the alternative supply shall be such that danger or damage
> to equipment does not arise after the connection or disconnection of any
> intended load as a result of the deviation of the voltage or frequency from the
> standard range. Means shall be provided to automatically disconnect such
> parts of the installation, as may be necessary if the capacity of the
> alternative supply is exceeded_


Any tips on devices that can be used to automatically disconnect heavy loads?

I have looked into no volt relays and solid state relays being switched using the higher frequncey remote devices.

Also wifi ... to unstable and boosters required at a cost. 

Bluetooth ... distances too far ... also boosters required.

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## GCE

A few of the inverters are coming out with voltage free contacts to be able to disconnect load on grid out .
No volt relays still the most reliable 
There are smart relays that will drop load when you draw more then say 20 Amps.

To me they all run the risk of failure and I rather ensure that the load on the inverter side is well within the ratings and loading that are needed which saves inverter life and battery life

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## Derlyn

> Provided of course that the full load from the municipality is not being switched through the change over switch, if the main supply is rated above the 35A.
> In my case I have a 3 phase 80Amp mains supply, where the whole load is switched through the change over switch when the generator runs.
> 
> The original 80A change over from ACDC, Neutral contact burnt out when it was running off the municipal supply, and we replaced it with the 100A.
> 
> So it depends, if you are only using it to switch a partial load at the site, then the 35A may be more than adequate.


Here in Emonti soon to be Egompo the mains is connected to the switch , the genny to the switch and 95% of the time, the houses DB is the load.

That's why I said I shudder to think how many under rated switches have been installed.

Peace out  ..  Derek

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