Hi,
You know those metal back boxes with oval knockouts, like
https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
Do you still need to grommet the top hole as it says it has been deburred?

Grumps <not@here.com> wrote:
> Hi,
> You know those metal back boxes with oval knockouts, like
> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
> Do you still need to grommet the top hole as it says it has been deburred?
>

I doubt you would get a grommet on the top entry as the edge has been
piened over so providing a smooth deburred edge. So the answer is - no!

Richard

On 17/07/2023 10:10, Grumps wrote:
> Hi,
> You know those metal back boxes with oval knockouts, like
> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
> Do you still need to grommet the top hole as it says it has been deburred?

You should still use a grommet - a normal 20mm round one will fit.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 17/07/2023 10:19, Tricky Dicky wrote:
> Grumps <not@here.com> wrote:
>> Hi,
>> You know those metal back boxes with oval knockouts, like
>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>> Do you still need to grommet the top hole as it says it has been deburred?
>>
>
> I doubt you would get a grommet on the top entry as the edge has been
> piened over so providing a smooth deburred edge. So the answer is - no!

A normal 20mm round grommet will still fit. About the only time I would
leave one out is if running oval trunking straight into the top...

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 17/07/2023 10:10, Grumps wrote:
> Hi,
> You know those metal back boxes with oval knockouts, like
> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
> Do you still need to grommet the top hole as it says it has been deburred?

Not answering the question but if you can fit a deeper backbox you may
have future options for dimmer or smart switches which may/will not fit
in a 16mm backbox.
--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 17/07/2023 12:35, alan_m wrote:
> On 17/07/2023 10:10, Grumps wrote:
>> Hi,
>> You know those metal back boxes with oval knockouts, like
>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>> Do you still need to grommet the top hole as it says it has been
>> deburred?
>
>
> Not answering the question but if you can fit a deeper backbox you may
> have future options for dimmer or smart switches which may/will not fit
> in a 16mm backbox.

The hole in the wall will take a 25mm box. I haven't found a 25mm with
an oval hole. But then, I'm crap at Google.

On 17/07/2023 15:36, Grumps wrote:
> On 17/07/2023 12:35, alan_m wrote:
>> On 17/07/2023 10:10, Grumps wrote:
>>> Hi,
>>> You know those metal back boxes with oval knockouts, like
>>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>>> Do you still need to grommet the top hole as it says it has been
>>> deburred?
>>
>>
>> Not answering the question but if you can fit a deeper backbox you may
>> have future options for dimmer or smart switches which may/will not
>> fit in a 16mm backbox.
>
> The hole in the wall will take a 25mm box. I haven't found a 25mm with
> an oval hole. But then, I'm crap at Google.

Is there any reason you need an oval hole? (you only normally see them
on slim boxes because there is not enough depth for a 20mm one, but they
need to get the total area up to something similar)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On Monday, 17 July 2023 at 15:37:01 UTC+1, Grumps wrote:
> On 17/07/2023 12:35, alan_m wrote:
> > On 17/07/2023 10:10, Grumps wrote:
> >> Hi,
> >> You know those metal back boxes with oval knockouts, like
> >> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
> >> Do you still need to grommet the top hole as it says it has been
> >> deburred?
> >
> >
> > Not answering the question but if you can fit a deeper backbox you may
> > have future options for dimmer or smart switches which may/will not fit
> > in a 16mm backbox.
> The hole in the wall will take a 25mm box. I haven't found a 25mm with
> an oval hole. But then, I'm crap at Google.

Mount your 16mm backbox recessed by 9mm and you've effectively got a 25mm box. OK if the wall material is nonflammable.

On 17/07/2023 18:39, John Rumm wrote:
> On 17/07/2023 15:36, Grumps wrote:
>> On 17/07/2023 12:35, alan_m wrote:
>>> On 17/07/2023 10:10, Grumps wrote:
>>>> Hi,
>>>> You know those metal back boxes with oval knockouts, like
>>>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>>>> Do you still need to grommet the top hole as it says it has been
>>>> deburred?
>>>
>>>
>>> Not answering the question but if you can fit a deeper backbox you
>>> may have future options for dimmer or smart switches which may/will
>>> not fit in a 16mm backbox.
>>
>> The hole in the wall will take a 25mm box. I haven't found a 25mm with
>> an oval hole. But then, I'm crap at Google.
>
> Is there any reason you need an oval hole? (you only normally see them
> on slim boxes because there is not enough depth for a 20mm one, but they
> need to get the total area up to something similar)

I'm replacing a back box with one that has an earth connection. The
existing box has been removed (and destroyed in the process), so please
don't say I could've added an earth to that box.
The current wiring is central to the existing box, and without doing any
more chiselling of the brickwork, I can't get the existing wires to go
to standard round knockout positions.

So, I don't necessarily need an oval holed one, but I haven't found any
with a centrally located round hole.

On 17/07/2023 21:07, Grumps wrote:
> On 17/07/2023 18:39, John Rumm wrote:
>> On 17/07/2023 15:36, Grumps wrote:
>>> On 17/07/2023 12:35, alan_m wrote:
>>>> On 17/07/2023 10:10, Grumps wrote:
>>>>> Hi,
>>>>> You know those metal back boxes with oval knockouts, like
>>>>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>>>>> Do you still need to grommet the top hole as it says it has been
>>>>> deburred?
>>>>
>>>>
>>>> Not answering the question but if you can fit a deeper backbox you
>>>> may have future options for dimmer or smart switches which may/will
>>>> not fit in a 16mm backbox.
>>>
>>> The hole in the wall will take a 25mm box. I haven't found a 25mm
>>> with an oval hole. But then, I'm crap at Google.
>>
>> Is there any reason you need an oval hole? (you only normally see them
>> on slim boxes because there is not enough depth for a 20mm one, but
>> they need to get the total area up to something similar)
>
> I'm replacing a back box with one that has an earth connection. The
> existing box has been removed (and destroyed in the process), so please
> don't say I could've added an earth to that box.
> The current wiring is central to the existing box, and without doing any
> more chiselling of the brickwork, I can't get the existing wires to go
> to standard round knockout positions.
>
> So, I don't necessarily need an oval holed one, but I haven't found any
> with a centrally located round hole.

If you can go deeper, then many of the 47mm deep boxes have a centre
hole (probably 25mm diameter)

https://www.tlc-direct.co.uk/Products/AP618.html

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 17/07/2023 21:39, John Rumm wrote:
> On 17/07/2023 21:07, Grumps wrote:
>> On 17/07/2023 18:39, John Rumm wrote:
>>> On 17/07/2023 15:36, Grumps wrote:
>>>> On 17/07/2023 12:35, alan_m wrote:
>>>>> On 17/07/2023 10:10, Grumps wrote:
>>>>>> Hi,
>>>>>> You know those metal back boxes with oval knockouts, like
>>>>>> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
>>>>>> Do you still need to grommet the top hole as it says it has been
>>>>>> deburred?
>>>>>
>>>>>
>>>>> Not answering the question but if you can fit a deeper backbox you
>>>>> may have future options for dimmer or smart switches which may/will
>>>>> not fit in a 16mm backbox.
>>>>
>>>> The hole in the wall will take a 25mm box. I haven't found a 25mm
>>>> with an oval hole. But then, I'm crap at Google.
>>>
>>> Is there any reason you need an oval hole? (you only normally see
>>> them on slim boxes because there is not enough depth for a 20mm one,
>>> but they need to get the total area up to something similar)
>>
>> I'm replacing a back box with one that has an earth connection. The
>> existing box has been removed (and destroyed in the process), so
>> please don't say I could've added an earth to that box.
>> The current wiring is central to the existing box, and without doing
>> any more chiselling of the brickwork, I can't get the existing wires
>> to go to standard round knockout positions.
>>
>> So, I don't necessarily need an oval holed one, but I haven't found
>> any with a centrally located round hole.
>
> If you can go deeper, then many of the 47mm deep boxes have a centre
> hole (probably 25mm diameter)
>
> https://www.tlc-direct.co.uk/Products/AP618.html

That's a thought, thanks.

I'll need to bash out another 20mm into the wall. The wall is thick
enough, but I don't want to redecorate afterwards.

On 17/07/2023 21:07, Grumps wrote:

>
> So, I don't necessarily need an oval holed one, but I haven't found any
> with a centrally located round hole.
>
>

The 16mm one you list hasn't got a centrally located hole for wires.
Depending on which backbox you buy you may find one with a 25mm round
knockout in the same location as the oval knockout in th one you list.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 17/07/2023 10:10, Grumps wrote:
> Hi,
> You know those metal back boxes with oval knockouts, like
> https://www.screwfix.com/p/appleby-1-gang-galvanised-steel-knockout-box-16mm/30573
> Do you still need to grommet the top hole as it says it has been deburred?

Do you have access to a Dremel and a carbide bit? Make your own hole by
enlarging the existing mounting hole?

On 18/07/2023 13:49, alan_m wrote:
> On 17/07/2023 21:07, Grumps wrote:
>
>>
>> So, I don't necessarily need an oval holed one, but I haven't found
>> any with a centrally located round hole.
>>
>>
>
> The 16mm one you list hasn't got a centrally located hole for wires.
> Depending on which backbox you buy you may find one with a 25mm round
> knockout in the same location as the oval knockout in th one you list.

Oh, OK.
What is the centrally located oval hole for?

On 18/07/2023 21:07, Grumps wrote:
> On 18/07/2023 13:49, alan_m wrote:
>> On 17/07/2023 21:07, Grumps wrote:
>>
>>>
>>> So, I don't necessarily need an oval holed one, but I haven't found
>>> any with a centrally located round hole.
>>>
>>>
>>
>> The 16mm one you list hasn't got a centrally located hole for wires.
>> Depending on which backbox you buy you may find one with a 25mm round
>> knockout in the same location as the oval knockout in th one you list.
>
> Oh, OK.
> What is the centrally located oval hole for?
>

Are you referring to the very small oval holes for the fixing screws?
You will not find a back-box grommet to fit those holes.

The holes for the wires are those knock-out positions where you remove
the metal and insert a grommet to protect the wire being cut by the metal.

What you could possible do is drill out the centre hole to 20mm with a
step drill to enable a standard grommet to be fitted. Knockouts come in
20mm and 25mm with grommets readily available for both sizes.

BTW when fitting a back box it is recommended that the terminal for the
earth wire is at the bottom. Possible not too important for a light
back-box but with a socket back-box nearer the floor it can be a
complete PITA to install the earth wire as you cannot see the terminal
unless you are physically low down, especially with deep back-boxes.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 19/07/2023 06:28, alan_m wrote:
> On 18/07/2023 21:07, Grumps wrote:
>> On 18/07/2023 13:49, alan_m wrote:
>>> On 17/07/2023 21:07, Grumps wrote:
>>>
>>>>
>>>> So, I don't necessarily need an oval holed one, but I haven't found
>>>> any with a centrally located round hole.
>>>>
>>>>
>>>
>>> The 16mm one you list hasn't got a centrally located hole for wires.
>>> Depending on which backbox you buy you may find one with a 25mm round
>>> knockout in the same location as the oval knockout in th one you list.
>>
>> Oh, OK.
>> What is the centrally located oval hole for?
>>
>
> Are you referring to the very small oval holes for the fixing screws?
> You will not find a back-box grommet to fit those holes.
>
> The holes for the wires are those knock-out positions where you remove
> the metal and insert a grommet to protect the wire being cut by the metal.
>
> What you could possible do is drill out the centre hole to 20mm with a
> step drill to enable a standard grommet to be fitted. Knockouts come in
> 20mm and 25mm with grommets readily available for both sizes.
>
> BTW when fitting a back box it is recommended that the terminal for the
> earth wire is at the bottom. Possible not too important for a light
> back-box but with a socket back-box nearer the floor it can be a
> complete PITA to install the earth wire as you cannot see the terminal
> unless you are physically low down, especially with deep back-boxes.

These holes:
https://ibb.co/87dXztj

Recommended to have earth terminal at bottom? Is that a regs thing or
just accessibility?

On 18/07/2023 13:49, alan_m wrote:
> On 17/07/2023 21:07, Grumps wrote:
>
>>
>> So, I don't necessarily need an oval holed one, but I haven't found
>> any with a centrally located round hole.
>>
>>
>
> The 16mm one you list hasn't got a centrally located hole for wires.

</panto_mode=on>

Oh yes it does (look at the angled photo)

</panto_mode=off>

> Depending on which backbox you buy you may find one with a 25mm round
> knockout in the same location as the oval knockout in th one you list.
>

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 19/07/2023 08:20, Grumps wrote:
> On 19/07/2023 06:28, alan_m wrote:
>> On 18/07/2023 21:07, Grumps wrote:
>>> On 18/07/2023 13:49, alan_m wrote:
>>>> On 17/07/2023 21:07, Grumps wrote:
>>>>
>>>>>
>>>>> So, I don't necessarily need an oval holed one, but I haven't found
>>>>> any with a centrally located round hole.
>>>>>
>>>>>
>>>>
>>>> The 16mm one you list hasn't got a centrally located hole for wires.
>>>> Depending on which backbox you buy you may find one with a 25mm
>>>> round knockout in the same location as the oval knockout in th one
>>>> you list.
>>>
>>> Oh, OK.
>>> What is the centrally located oval hole for?
>>>
>>
>> Are you referring to the very small oval holes for the fixing screws?
>> You will not find a back-box grommet to fit those holes.
>>
>> The holes for the wires are those knock-out positions where you remove
>> the metal and insert a grommet to protect the wire being cut by the
>> metal.
>>
>> What you could possible do is drill out the centre hole to 20mm with a
>> step drill to enable a standard grommet to be fitted. Knockouts come
>> in 20mm and 25mm with grommets readily available for both sizes.
>>
>> BTW when fitting a back box it is recommended that the terminal for
>> the earth wire is at the bottom. Possible not too important for a
>> light back-box but with a socket back-box nearer the floor it can be a
>> complete PITA to install the earth wire as you cannot see the terminal
>> unless you are physically low down, especially with deep back-boxes.
>
> These holes:
> https://ibb.co/87dXztj
>
> Recommended to have earth terminal at bottom? Is that a regs thing or
> just accessibility?

I was not aware of any recommendation as to its location.

Note that an earth terminal on a metal back box is not actually required
unless both screw lugs for the accessory are adjustable. Typically one
is fixed, and thus you can rely on the screw connecting to the accessory
to connect the box to earth.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 19/07/2023 11:56, John Rumm wrote:
> On 19/07/2023 08:20, Grumps wrote:
>> On 19/07/2023 06:28, alan_m wrote:
>>> On 18/07/2023 21:07, Grumps wrote:
>>>> On 18/07/2023 13:49, alan_m wrote:
>>>>> On 17/07/2023 21:07, Grumps wrote:
>>>>>
>>>>>>
>>>>>> So, I don't necessarily need an oval holed one, but I haven't
>>>>>> found any with a centrally located round hole.
>>>>>>
>>>>>>
>>>>>
>>>>> The 16mm one you list hasn't got a centrally located hole for
>>>>> wires. Depending on which backbox you buy you may find one with a
>>>>> 25mm round knockout in the same location as the oval knockout in th
>>>>> one you list.
>>>>
>>>> Oh, OK.
>>>> What is the centrally located oval hole for?
>>>>
>>>
>>> Are you referring to the very small oval holes for the fixing screws?
>>> You will not find a back-box grommet to fit those holes.
>>>
>>> The holes for the wires are those knock-out positions where you
>>> remove the metal and insert a grommet to protect the wire being cut
>>> by the metal.
>>>
>>> What you could possible do is drill out the centre hole to 20mm with
>>> a step drill to enable a standard grommet to be fitted. Knockouts
>>> come in 20mm and 25mm with grommets readily available for both sizes.
>>>
>>> BTW when fitting a back box it is recommended that the terminal for
>>> the earth wire is at the bottom. Possible not too important for a
>>> light back-box but with a socket back-box nearer the floor it can be
>>> a complete PITA to install the earth wire as you cannot see the
>>> terminal unless you are physically low down, especially with deep
>>> back-boxes.
>>
>> These holes:
>> https://ibb.co/87dXztj
>>
>> Recommended to have earth terminal at bottom? Is that a regs thing or
>> just accessibility?
>
> I was not aware of any recommendation as to its location.
>
> Note that an earth terminal on a metal back box is not actually required
> unless both screw lugs for the accessory are adjustable. Typically one
> is fixed, and thus you can rely on the screw connecting to the accessory
> to connect the box to earth.
>

That's not going to work if the OP has a plastic light switch.