The recommended way, is to connect the redcare wiring to the A+B ports on the backplate of the NTE5C, where the incoming feed is connected also.
I have only recently become aware of this as for years now, I (and I suspect many, many other engineers) have removed the redcare wiring from the backplate, and reconnected to the extension wiring ports at the front, and fit the MK4 SSFP to 'isolate' the alarm.
This has proven to pay massive dividends, historically ..... but apparently the latest brief is that only non-redcare alarm dialling systems should be connected to the front-mounted ports, and that redcare should always be connected to the A+B ports at the rear ... along with a new filter that we have been given the item code for. In other words, we fit the filter in the NTE, as opposed to the alarm company fitting one within their panel.
My only caveat is that this is a very new process that I haven't used in anger, and am getting this info second-hand, albeit from a great source.