Does the External Junction Box have to be fitted outside on the wall, or can it be fitted internally?
If fitted outside on the wall, does the Optical Network Terminal (ONT) have to be fitted directly on the other side of the wall, or can it be fitted in another room?
The CSP ( customer service point ) is usually fitted externally, although an internal version is available it’s not the default option and won’t be offered on the installation day , the reason to have the CSP fitted externally is so access into the house for testing / fault location isn’t required , the ONT doesn’t have on the internal wall opposite the location of the external CSP , but the installer won’t consider impractical or overly time consuming locations for the ONT to be fitted .
If the ONT (for example) is required at the rear of the property but the CSP is fitted at the front of the property the optical cable between the two would be external cable on wall , not ran internally.
What is the reason that you would like the ONT in a different room?
The ONT and the router / SmartHub do not have to be in the same place. The connection between the two is by ethernet cable.
Provided a cable of spec CAT5E or higher is used, (note the "E" suffix, it is important), the ONT and router can be up to 100 metres apart, though keeping it to less than 80 metres is recommended.
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The Lead In from the CSP to the ONT comes in pre-made lengths from the Factory ranging from 5m to 50m so no, the CSP and ONT don’t have to go on the wall adjacent to each other.