About 115 customers are expected to go without power on the 37 degree day. Police and Emergency Services Minister Mick Gentleman said the government asked ActewAGL to look into rescheduling its works but was told the maintenance was "essential".

The government can only intervene when its Extreme Heat Plan is activated, which would require the mean temperature over a 24 hour period to be equal to or greater than 28 degrees over three consecutive days.

ActewAGLsaid on Thursday it would work as quickly as possible to restore power by Friday lunchtime.

"ActewAGL have also advised the government that residents have been informed of the planned outage and that the ACT Emergency Services Agency are ready and taking all precautions, they are working with ActewAGL to ensure that health of known vulnerable residents in the affected areas is not compromised," Mr Gentleman said.

Unions and workers have also raised the alarm on the impact the heat will have and called on the company to defer its maintenance to prevent heat-related incidents.

Electrical Trades Union organiser Mick Koppie was worried workers would feel rushed to complete work in the heat by ActewAGL or face negative community feedback if they followed heat safety policy by resting every hour.

"The customers will be looking straight at them wondering why aren't you getting my airconditioning on," Mr Koppie said.

"The main concerns are firstly the customers, and secondly the guys who are going to be doing the work being pushed and having to breach policy simply to get the power back on to the customers and it's not an emergency or fault."

ActewAGL said the works were critical and asked for customer understanding as workers were required to rest one full hour for every hour worked in temperatures above 36 degrees.

An ActewAGL employee involved in Friday's maintenance, who asked not be identified, said internal emails at ActewAGL expecting before-schedule completion and an immediate report had put pressure on the 15-20 strong work crew to rush maintenance on the unseasonably hot day.

"I can also tell you that the work that we have for our team is not do or die," the worker said. "They're putting blokes at risk for no real reason."

The company said pole replacement in Hawker could be rescheduled if the work would take longer than planned, but critical vegetation management was required in Hughes.

It is understood the worker is part of the crew attending to the work in Hawker.

ActewAGL did not tell workers to ignore the normal safety procedures regarding working in the heat.

ActewAGL official Clinton McAlister said on Thursday the utility considered the wellbeing of the work crews but if work was delayed it risked unplanned blackouts and network damage, while rescheduling or cancelling works came at a cost.

"We don't make these decisions lightly," he said.

"The work is now scheduled to be completed well before the forecast maximum temperature for tomorrow."

In NSW's central coast, the state energy provider Ausgrid cancelled planned outages on Monday due to 40C degree heat.

A spokesperson for Ausgrid said the company reviewed interruptions when high temperatures were forecast, taking the potential impact on customers into consideration.

The ActewAGL worker said if they completed the Hawker maintenance ahead of schedule, stopping every hour as expected wouldn't be possible, increasing the risk of heat related injuries or mistakes by workers due to fatigue.

The worker was also concerned about the affected customers, especially any elderly living in the areas.

Mr Koppie suggested cost cutting procedures at ActewAGL led to pressure on the company to deliver despite risks.

"If the stars don't align mate, they try to align them," the worker said.

Mr Koppie said pole replacement works in Tumut, NSW had been completed between 11pm and 5am to avoid inconvenience for customers and proposed ActewAGL did the same, but said maybe the company had considered overtime too costly.

ActewAGL said Friday's maintenance could only be completed during daylight hours for health and safety reasons.

- with Emily Baker